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Move __libc_int0x80 to an assembly file

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Bug: http://b/157081822

If __libc_int0x80 is in a C/C++ file, Clang's coverage instrumentation
adds instructions to count the number of times it gets executed [1].
With coverage instrumentation, __libc_sysinfo, used on 32-bit x86, is
initialized to the wrong value, causing dl.preinit_system_calls to fail.

Moving the function to an assembly file leaves __libc_sysinfo properly
initialized.

[1] We could change clang so it doesn't instrument functions marked
__attribute__((naked)) as a followup.

Test: `m CLANG_COVERAGE=true NATIVE_COVERAGE_PATHS=bionic` and run
bionic-unit-tests

Change-Id: I73558253512392d345de8d5b66d38bb14b308fdf
This commit is contained in:
Pirama Arumuga Nainar 2021-02-12 15:09:49 -08:00
parent 332065d57e
commit 7b89be78f4
4 changed files with 9 additions and 5 deletions
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1
libc/Android.bp
View file

@ -170,6 +170,7 @@ cc_library_static {
x86: {
srcs: [
"arch-x86/bionic/__libc_init_sysinfo.cpp",
"arch-x86/bionic/__libc_int0x80.S",
"arch-x86/bionic/__set_tls.cpp",
],
},

4
libc/arch-x86/bionic/__libc_init_sysinfo.cpp
View file

@ -32,10 +32,6 @@
// This file is compiled without stack protection, because it runs before TLS
// has been set up.
__LIBC_HIDDEN__ __attribute__((__naked__)) void __libc_int0x80() {
__asm__ volatile("int $0x80; ret");
}
__LIBC_HIDDEN__ void __libc_init_sysinfo() {
bool unused;
__libc_sysinfo = reinterpret_cast<void*>(__bionic_getauxval(AT_SYSINFO, &unused));

7
libc/arch-x86/bionic/__libc_int0x80.S Normal file
View file

@ -0,0 +1,7 @@
#include <private/bionic_asm.h>
// void __libc_int0x80();
ENTRY_PRIVATE(__libc_int0x80)
int $0x80
ret
END(__libc_int0x80)

2
libc/private/bionic_globals.h
View file

@ -123,7 +123,7 @@ __LIBC_HIDDEN__ void __libc_init_vdso(libc_globals* globals);
#if defined(__i386__)
__LIBC_HIDDEN__ extern void* __libc_sysinfo;
__LIBC_HIDDEN__ void __libc_int0x80();
extern "C" __LIBC_HIDDEN__ void __libc_int0x80();
__LIBC_HIDDEN__ void __libc_init_sysinfo();
#endif