From ffd0f69c375f12f081a1a5158a02a05000b7a93c Mon Sep 17 00:00:00 2001

From: Vitaly Buka <vitalybuka@google.com>

Date: Fri, 16 Apr 2021 09:50:24 -0700

Subject: [PATCH][compiler-rt] Sanitizer built against glibc 2.34 doesn't work

As mentioned in https://gcc.gnu.org/PR100114 , glibc starting with the

https://sourceware.org/git/?p=glibc.git;a=commit;h=6c57d320484988e87e446e2e60ce42816bf51d53

change doesn't define SIGSTKSZ and MINSIGSTKSZ macros to constants, but to sysconf function call.

sanitizer_posix_libcdep.cpp has

static const uptr kAltStackSize = SIGSTKSZ * 4;  // SIGSTKSZ is not enough.

which is generally fine, just means that when SIGSTKSZ is not a compile time constant will be initialized later.

The problem is that kAltStackSize is used in SetAlternateSignalStack which is called very early, from .preinit_array

initialization, i.e. far before file scope variables are constructed, which means it is not initialized and

mmapping 0 will fail:

==145==ERROR: AddressSanitizer failed to allocate 0x0 (0) bytes of SetAlternateSignalStack (error code: 22)

Here is one possible fix, another one could be to make kAltStackSize a preprocessor macro if _SG_SIGSTKSZ is defined

(but perhaps with having an automatic const variable initialized to it so that sysconf isn't at least called twice

during SetAlternateSignalStack.

Reviewed By: vitalybuka

Differential Revision: https://reviews.llvm.org/D100645

(cherry picked from commit 82150606fb11d28813ae6da1101f5bda638165fe)

---

 compiler-rt/lib/sanitizer_common/sanitizer_posix_libcdep.cpp | 12 ++++++++----

 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_posix_libcdep.cpp b/compiler-rt/lib/sanitizer_common/sanitizer_posix_libcdep.cpp

index d29438c..2b10bdd 100644

--- a/compiler-rt/lib/sanitizer_common/sanitizer_posix_libcdep.cpp

+++ b/compiler-rt/lib/sanitizer_common/sanitizer_posix_libcdep.cpp

@@ -165,7 +165,11 @@ bool SupportsColoredOutput(fd_t fd) {

 #if !SANITIZER_GO

 // TODO(glider): different tools may require different altstack size.

-static const uptr kAltStackSize = SIGSTKSZ * 4;  // SIGSTKSZ is not enough.

+static uptr GetAltStackSize() {

+  // SIGSTKSZ is not enough.

+  static const uptr kAltStackSize = SIGSTKSZ * 4;

+  return kAltStackSize;

+}

 void SetAlternateSignalStack() {

   stack_t altstack, oldstack;

@@ -176,10 +180,10 @@ void SetAlternateSignalStack() {

   // TODO(glider): the mapped stack should have the MAP_STACK flag in the

   // future. It is not required by man 2 sigaltstack now (they're using

   // malloc()).

-  void* base = MmapOrDie(kAltStackSize, __func__);

+  void *base = MmapOrDie(GetAltStackSize(), __func__);

   altstack.ss_sp = (char*) base;

   altstack.ss_flags = 0;

-  altstack.ss_size = kAltStackSize;

+  altstack.ss_size = GetAltStackSize();

   CHECK_EQ(0, sigaltstack(&altstack, nullptr));

 }

@@ -187,7 +191,7 @@ void UnsetAlternateSignalStack() {

   stack_t altstack, oldstack;

   altstack.ss_sp = nullptr;

   altstack.ss_flags = SS_DISABLE;

-  altstack.ss_size = kAltStackSize;  // Some sane value required on Darwin.

+  altstack.ss_size = GetAltStackSize();  // Some sane value required on Darwin.

   CHECK_EQ(0, sigaltstack(&altstack, &oldstack));

   UnmapOrDie(oldstack.ss_sp, oldstack.ss_size);

 }

-- 

1.8.3.1