pub_soft/abseil-cpp
3
0
Fork 0
mirror of https://github.com/abseil/abseil-cpp.git synced 2026-06-04 12:07:05 +08:00
Code Issues Packages Projects Releases Wiki Activity

AddressIsReadable: improve comments

Browse Source 
Linux kernel's rt_sigprocmask correctly handles an unaligned user address[1].
The original issue was for qemu-user, which seems long irrelevant.

Tested locally on an AArch64 CPU and qemu-aarch64-static.

The alignment operation actually serves another purpose: when addr resides in
the last 7 bytes of a page (unaligned), check only the current page and not the
next. Update the comment.

[1]:
kernel/signal.c `SYSCALL_DEFINE4(rt_sigprocmask`
arch/arm64/include/asm/uaccess.h:raw_copy_from_user
arch/arm64/lib/copy_template.S  "alignment handled by the hardware"

PiperOrigin-RevId: 592618320
Change-Id: Ifbd05aba42f46e36e710cca940570213036b3ce0
This commit is contained in:
Fangrui Song
2023-12-20 11:47:37 -08:00
committed by Copybara-Service
parent 299dbc588e
commit 7a1898a04f
1 changed files with 4 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files

6
absl/debugging/internal/address_is_readable.cc
View File

@@ -50,8 +50,10 @@ namespace debugging_internal {
// NOTE: any new system calls here may also require sandbox reconfiguration.
//
bool AddressIsReadable(const void *addr) {
// Align address on 8-byte boundary. On aarch64, checking last
// byte before inaccessible page returned unexpected EFAULT.
// rt_sigprocmask below checks 8 contiguous bytes. If addr resides in the
// last 7 bytes of a page (unaligned), rt_sigprocmask would additionally
// check the readability of the next page, which is not desired. Align
// address on 8-byte boundary to check only the current page.
const uintptr_t u_addr = reinterpret_cast<uintptr_t>(addr) & ~uintptr_t{7};
addr = reinterpret_cast<const void *>(u_addr);