Blame SOURCES/0254-modules-load-module-sections-at-page-aligned-address.patch

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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Peter Jones <pjones@redhat.com>
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Date: Mon, 21 Mar 2022 17:45:40 -0400
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Subject: [PATCH] modules: load module sections at page-aligned addresses
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Currently we load module sections at whatever alignment gcc+ld happened
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to dump into the ELF section header, which is often pretty useless.  For
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example, by default time.mod has these sections on a current x86_64
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build:
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$ eu-readelf -a grub-core/time.mod |& grep ^Section -A13
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Section Headers:
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[Nr] Name            Type         Addr  Off      Size     ES Flags Lk Inf Al
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[ 0]                 NULL         0     00000000 00000000  0        0   0  0
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[ 1] .text           PROGBITS     0     00000040 0000015e  0 AX     0   0  1
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[ 2] .rela.text      RELA         0     00000458 000001e0 24 I      8   1  8
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[ 3] .rodata.str1.1  PROGBITS     0     0000019e 000000a1  1 AMS    0   0  1
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[ 4] .module_license PROGBITS     0     00000240 0000000f  0 A      0   0  8
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[ 5] .data           PROGBITS     0     0000024f 00000000  0 WA     0   0  1
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[ 6] .bss            NOBITS       0     00000250 00000008  0 WA     0   0  8
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[ 7] .modname        PROGBITS     0     00000250 00000005  0        0   0  1
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[ 8] .symtab         SYMTAB       0     00000258 00000150 24        9   6  8
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[ 9] .strtab         STRTAB       0     000003a8 000000ab  0        0   0  1
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[10] .shstrtab       STRTAB       0     00000638 00000059  0        0   0  1
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With NX protections being page based, loading sections with either a 1
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or 8 *byte* alignment does absolutely nothing to help us out.
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This patch switches most EFI platforms to load module sections at 4kB
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page-aligned addresses.  To do so, it adds an new per-arch function,
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grub_arch_dl_min_alignment(), which returns the alignment needed for
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dynamically loaded sections (in bytes).  Currently it sets it to 4096
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when GRUB_MACHINE_EFI is true on x86_64, i386, arm, arm64, and emu, and
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1-byte alignment on everything else.
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It then changes the allocation size computation and the loader code in
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grub_dl_load_segments() to align the locations and sizes up to these
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boundaries, and fills any added padding with zeros.
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All of this happens before relocations are applied, so the relocations
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factor that in with no change.
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As an aside, initially Daniel Kiper and I thought that it might be a
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better idea to split the modules up into top-level sections as
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.text.modules, .rodata.modules, .data.modules, etc., so that their page
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permissions would get set by the loader that's loading grub itself.
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This turns out to have two significant downsides: 1) either in mkimage
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or in grub_dl_relocate_symbols(), you wind up having to dynamically
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process the relocations to accommodate the moved module sections, and 2)
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you then need to change the permissions on the modules and change them
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back while relocating them in grub_dl_relocate_symbols(), which means
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that any loader that /does/ honor the section flags but does /not/
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generally support NX with the memory attributes API will cause grub to
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fail.
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Signed-off-by: Peter Jones <pjones@redhat.com>
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---
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 grub-core/kern/arm/dl.c     | 13 +++++++++++++
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 grub-core/kern/arm64/dl.c   | 13 +++++++++++++
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 grub-core/kern/dl.c         | 29 +++++++++++++++++++++--------
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 grub-core/kern/emu/full.c   | 13 +++++++++++++
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 grub-core/kern/i386/dl.c    | 13 +++++++++++++
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 grub-core/kern/ia64/dl.c    |  9 +++++++++
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 grub-core/kern/mips/dl.c    |  8 ++++++++
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 grub-core/kern/powerpc/dl.c |  9 +++++++++
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 grub-core/kern/riscv/dl.c   | 13 +++++++++++++
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 grub-core/kern/sparc64/dl.c |  9 +++++++++
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 grub-core/kern/x86_64/dl.c  | 13 +++++++++++++
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 include/grub/dl.h           |  2 ++
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 docs/grub-dev.texi          |  6 +++---
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 13 files changed, 139 insertions(+), 11 deletions(-)
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diff --git a/grub-core/kern/arm/dl.c b/grub-core/kern/arm/dl.c
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index eab9d17ff2..9260737936 100644
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--- a/grub-core/kern/arm/dl.c
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+++ b/grub-core/kern/arm/dl.c
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@@ -278,3 +278,16 @@ grub_arch_dl_check_header (void *ehdr)
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   return GRUB_ERR_NONE;
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 }
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+
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+/*
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+ * Tell the loader what our minimum section alignment is.
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+ */
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+grub_size_t
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+grub_arch_dl_min_alignment (void)
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+{
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+#ifdef GRUB_MACHINE_EFI
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+  return 4096;
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+#else
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+  return 1;
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+#endif
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+}
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diff --git a/grub-core/kern/arm64/dl.c b/grub-core/kern/arm64/dl.c
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index 512e5a80b0..0d4a26857f 100644
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--- a/grub-core/kern/arm64/dl.c
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+++ b/grub-core/kern/arm64/dl.c
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@@ -196,3 +196,16 @@ grub_arch_dl_relocate_symbols (grub_dl_t mod, void *ehdr,
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   return GRUB_ERR_NONE;
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 }
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+
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+/*
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+ * Tell the loader what our minimum section alignment is.
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+ */
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+grub_size_t
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+grub_arch_dl_min_alignment (void)
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+{
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+#ifdef GRUB_MACHINE_EFI
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+  return 4096;
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+#else
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+  return 1;
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+#endif
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+}
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diff --git a/grub-core/kern/dl.c b/grub-core/kern/dl.c
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index aef8af8aa7..8c7aacef39 100644
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--- a/grub-core/kern/dl.c
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+++ b/grub-core/kern/dl.c
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@@ -277,7 +277,7 @@ grub_dl_load_segments (grub_dl_t mod, const Elf_Ehdr *e)
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 {
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   unsigned i;
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   const Elf_Shdr *s;
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-  grub_size_t tsize = 0, talign = 1;
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+  grub_size_t tsize = 0, talign = 1, arch_addralign = 1;
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 #if !defined (__i386__) && !defined (__x86_64__) && !defined(__riscv)
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   grub_size_t tramp;
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   grub_size_t got;
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@@ -285,16 +285,24 @@ grub_dl_load_segments (grub_dl_t mod, const Elf_Ehdr *e)
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 #endif
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   char *ptr;
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+  arch_addralign = grub_arch_dl_min_alignment ();
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+
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   for (i = 0, s = (const Elf_Shdr *)((const char *) e + e->e_shoff);
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        i < e->e_shnum;
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        i++, s = (const Elf_Shdr *)((const char *) s + e->e_shentsize))
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     {
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+      grub_size_t sh_addralign;
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+      grub_size_t sh_size;
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+
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       if (s->sh_size == 0 || !(s->sh_flags & SHF_ALLOC))
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 	continue;
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-      tsize = ALIGN_UP (tsize, s->sh_addralign) + s->sh_size;
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-      if (talign < s->sh_addralign)
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-	talign = s->sh_addralign;
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+      sh_addralign = ALIGN_UP(s->sh_addralign, arch_addralign);
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+      sh_size = ALIGN_UP(s->sh_size, sh_addralign);
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+
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+      tsize = ALIGN_UP (tsize, sh_addralign) + sh_size;
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+      if (talign < sh_addralign)
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+	talign = sh_addralign;
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     }
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 #if !defined (__i386__) && !defined (__x86_64__) && !defined(__riscv)
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@@ -323,6 +331,9 @@ grub_dl_load_segments (grub_dl_t mod, const Elf_Ehdr *e)
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        i < e->e_shnum;
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        i++, s = (Elf_Shdr *)((char *) s + e->e_shentsize))
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     {
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+      grub_size_t sh_addralign = ALIGN_UP(s->sh_addralign, arch_addralign);
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+      grub_size_t sh_size = ALIGN_UP(s->sh_size, sh_addralign);
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+
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       if (s->sh_flags & SHF_ALLOC)
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 	{
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 	  grub_dl_segment_t seg;
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@@ -335,17 +346,19 @@ grub_dl_load_segments (grub_dl_t mod, const Elf_Ehdr *e)
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 	    {
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 	      void *addr;
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-	      ptr = (char *) ALIGN_UP ((grub_addr_t) ptr, s->sh_addralign);
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+	      ptr = (char *) ALIGN_UP ((grub_addr_t) ptr, sh_addralign);
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 	      addr = ptr;
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-	      ptr += s->sh_size;
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+	      ptr += sh_size;
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 	      switch (s->sh_type)
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 		{
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 		case SHT_PROGBITS:
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 		  grub_memcpy (addr, (char *) e + s->sh_offset, s->sh_size);
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+		  grub_memset ((char *)addr + s->sh_size, 0,
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+			       sh_size - s->sh_size);
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 		  break;
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 		case SHT_NOBITS:
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-		  grub_memset (addr, 0, s->sh_size);
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+		  grub_memset (addr, 0, sh_size);
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 		  break;
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 		}
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@@ -354,7 +367,7 @@ grub_dl_load_segments (grub_dl_t mod, const Elf_Ehdr *e)
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 	  else
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 	    seg->addr = 0;
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-	  seg->size = s->sh_size;
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+	  seg->size = sh_size;
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 	  seg->section = i;
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 	  seg->next = mod->segment;
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 	  mod->segment = seg;
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diff --git a/grub-core/kern/emu/full.c b/grub-core/kern/emu/full.c
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index e8d63b1f5f..1de1c28eb0 100644
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--- a/grub-core/kern/emu/full.c
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+++ b/grub-core/kern/emu/full.c
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@@ -67,3 +67,16 @@ grub_arch_dl_init_linker (void)
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 }
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 #endif
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+
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+/*
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+ * Tell the loader what our minimum section alignment is.
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+ */
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+grub_size_t
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+grub_arch_dl_min_alignment (void)
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+{
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+#ifdef GRUB_MACHINE_EFI
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+  return 4096;
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+#else
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+  return 1;
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+#endif
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+}
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diff --git a/grub-core/kern/i386/dl.c b/grub-core/kern/i386/dl.c
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index 1346da5cc9..d6b4681fc9 100644
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--- a/grub-core/kern/i386/dl.c
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+++ b/grub-core/kern/i386/dl.c
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@@ -79,3 +79,16 @@ grub_arch_dl_relocate_symbols (grub_dl_t mod, void *ehdr,
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   return GRUB_ERR_NONE;
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 }
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+
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+/*
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+ * Tell the loader what our minimum section alignment is.
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+ */
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+grub_size_t
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+grub_arch_dl_min_alignment (void)
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+{
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+#ifdef GRUB_MACHINE_EFI
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+  return 4096;
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+#else
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+  return 1;
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+#endif
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+}
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diff --git a/grub-core/kern/ia64/dl.c b/grub-core/kern/ia64/dl.c
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index db59300fea..92d82c5750 100644
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--- a/grub-core/kern/ia64/dl.c
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+++ b/grub-core/kern/ia64/dl.c
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@@ -148,3 +148,12 @@ grub_arch_dl_relocate_symbols (grub_dl_t mod, void *ehdr,
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     }
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   return GRUB_ERR_NONE;
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 }
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+
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+/*
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+ * Tell the loader what our minimum section alignment is.
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+ */
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+grub_size_t
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+grub_arch_dl_min_alignment (void)
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+{
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+  return 1;
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+}
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diff --git a/grub-core/kern/mips/dl.c b/grub-core/kern/mips/dl.c
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index 5d7d299c74..6d83bd71e9 100644
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--- a/grub-core/kern/mips/dl.c
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+++ b/grub-core/kern/mips/dl.c
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@@ -272,3 +272,11 @@ grub_arch_dl_init_linker (void)
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   grub_dl_register_symbol ("_gp_disp", &_gp_disp_dummy, 0, 0);
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 }
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+/*
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+ * Tell the loader what our minimum section alignment is.
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+ */
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+grub_size_t
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+grub_arch_dl_min_alignment (void)
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+{
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+  return 1;
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+}
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diff --git a/grub-core/kern/powerpc/dl.c b/grub-core/kern/powerpc/dl.c
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index cdd61b305f..5d9ba2e158 100644
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--- a/grub-core/kern/powerpc/dl.c
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+++ b/grub-core/kern/powerpc/dl.c
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@@ -167,3 +167,12 @@ grub_arch_dl_relocate_symbols (grub_dl_t mod, void *ehdr,
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   return GRUB_ERR_NONE;
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 }
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+
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+/*
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+ * Tell the loader what our minimum section alignment is.
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+ */
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+grub_size_t
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+grub_arch_dl_min_alignment (void)
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+{
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+  return 1;
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+}
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diff --git a/grub-core/kern/riscv/dl.c b/grub-core/kern/riscv/dl.c
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index f26b12aaa4..aa18f9e990 100644
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--- a/grub-core/kern/riscv/dl.c
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+++ b/grub-core/kern/riscv/dl.c
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@@ -343,3 +343,16 @@ grub_arch_dl_relocate_symbols (grub_dl_t mod, void *ehdr,
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   return GRUB_ERR_NONE;
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 }
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+
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+/*
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+ * Tell the loader what our minimum section alignment is.
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+ */
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+grub_size_t
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+grub_arch_dl_min_alignment (void)
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+{
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+#ifdef GRUB_MACHINE_EFI
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+  return 4096;
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+#else
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+  return 1;
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+#endif
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+}
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diff --git a/grub-core/kern/sparc64/dl.c b/grub-core/kern/sparc64/dl.c
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index f3d960186b..f054f08241 100644
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--- a/grub-core/kern/sparc64/dl.c
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+++ b/grub-core/kern/sparc64/dl.c
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@@ -189,3 +189,12 @@ grub_arch_dl_relocate_symbols (grub_dl_t mod, void *ehdr,
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   return GRUB_ERR_NONE;
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 }
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+
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+/*
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+ * Tell the loader what our minimum section alignment is.
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+ */
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+grub_size_t
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+grub_arch_dl_min_alignment (void)
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+{
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+  return 1;
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+}
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diff --git a/grub-core/kern/x86_64/dl.c b/grub-core/kern/x86_64/dl.c
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index e5a8bdcf4f..a105dc50ce 100644
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--- a/grub-core/kern/x86_64/dl.c
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+++ b/grub-core/kern/x86_64/dl.c
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@@ -119,3 +119,16 @@ grub_arch_dl_relocate_symbols (grub_dl_t mod, void *ehdr,
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   return GRUB_ERR_NONE;
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 }
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+
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+/*
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+ * Tell the loader what our minimum section alignment is.
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+ */
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+grub_size_t
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+grub_arch_dl_min_alignment (void)
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+{
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+#ifdef GRUB_MACHINE_EFI
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+  return 4096;
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+#else
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+  return 1;
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+#endif
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+}
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diff --git a/include/grub/dl.h b/include/grub/dl.h
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index 618ae6f474..f36ed5cb17 100644
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--- a/include/grub/dl.h
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+++ b/include/grub/dl.h
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@@ -280,6 +280,8 @@ grub_err_t grub_arch_dl_check_header (void *ehdr);
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 grub_err_t
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 grub_arch_dl_relocate_symbols (grub_dl_t mod, void *ehdr,
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 			       Elf_Shdr *s, grub_dl_segment_t seg);
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+grub_size_t
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+grub_arch_dl_min_alignment (void);
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 #endif
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 #if defined (_mips)
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diff --git a/docs/grub-dev.texi b/docs/grub-dev.texi
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index 19f708ee66..7b2455a8fe 100644
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--- a/docs/grub-dev.texi
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+++ b/docs/grub-dev.texi
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@@ -755,9 +755,9 @@ declare startup asm file ($cpu_$platform_startup) as well as any other files
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 (e.g. init.c and callwrap.S) (e.g. $cpu_$platform = kern/$cpu/$platform/init.c).
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 At this stage you will also need to add dummy dl.c and cache.S with functions
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 grub_err_t grub_arch_dl_check_header (void *ehdr), grub_err_t
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-grub_arch_dl_relocate_symbols (grub_dl_t mod, void *ehdr) (dl.c) and
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-void grub_arch_sync_caches (void *address, grub_size_t len) (cache.S). They
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-won't be used for now.
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+grub_arch_dl_relocate_symbols (grub_dl_t mod, void *ehdr) (dl.c), grub_uint32_t
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+grub_arch_dl_min_alignment (void), and void grub_arch_sync_caches (void
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+*address, grub_size_t len) (cache.S). They won't be used for now.
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 You will need to create directory include/$cpu/$platform and a file
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 include/$cpu/types.h. The later folowing this template: