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authorThirumalai Nagalingam <thirumalai.nagalingam@multicorewareinc.com>2025-07-01 18:17:24 +0000
committerJeremy Drake <cygwin@jdrake.com>2025-07-01 13:03:47 -0700
commit10380e9f446640c8d1bd4d60ec085bb31efa26f1 (patch)
tree05944e08456570d41158202bf90eb40269315acd
parent476135a24506dd624eb46b50fd634fcd740008ba (diff)
downloadnewlib-master.zip
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Cygwin: Aarch64: optimize pthread_wrapper register usageHEADmastermain
This patch resolves issues related to unsafe access to deallocated stack memory in the pthread wrapper for AArch64. Key changes: - Removed use of x19 by directly loading the thread function and argument using LDP from [WRAPPER_ARG], freeing one register. - Stored thread function and argument in x20 and x21 before VirtualFree to preserve them across calls. - Used x1 as a temporary register to load the stack base, subtract CYGTLS, and update SP. - Moved the thread argument back into x0 after VirtualFree and before calling the thread function. Earlier, `wrapper_arg` lived on the stack, which was freed via `VirtualFree`, risking segfaults on later access. Now, the thread `func` and `arg` are loaded before the stack is freed, stored in callee-saved registers, and restored to `x0` before calling the thread function. Fixes: f4ba145056db ("Aarch64: Add inline assembly pthread wrapper") Signed-off-by: Thirumalai Nagalingam <thirumalai.nagalingam@multicorewareinc.com>
-rw-r--r--winsup/cygwin/create_posix_thread.cc21
1 files changed, 11 insertions, 10 deletions
diff --git a/winsup/cygwin/create_posix_thread.cc b/winsup/cygwin/create_posix_thread.cc
index 592aaf1..17bb607 100644
--- a/winsup/cygwin/create_posix_thread.cc
+++ b/winsup/cygwin/create_posix_thread.cc
@@ -103,18 +103,19 @@ pthread_wrapper (PVOID arg)
/* Sets up a new thread stack, frees the original OS stack,
* and calls the thread function with its arg using AArch64 ABI. */
__asm__ __volatile__ ("\n\
- mov x19, %[WRAPPER_ARG] // x19 = &wrapper_arg \n\
- ldp x0, x10, [x19, #16] // x0 = stackaddr, x10 = stackbase \n\
- sub sp, x10, %[CYGTLS] // sp = stackbase - (CYGTLS) \n\
- mov fp, xzr // clear frame pointer (x29) \n\
- mov x1, xzr // x1 = 0 (dwSize) \n\
- mov x2, #0x8000 // x2 = MEM_RELEASE \n\
- bl VirtualFree // free original stack \n\
- ldp x19, x0, [x19] // x19 = func, x0 = arg \n\
- blr x19 // call thread function \n"
+ ldp x20, x21, [%[WRAPPER_ARG]] // x20 = thread func, x21 = thread arg \n\
+ ldp x0, x1, [%[WRAPPER_ARG], #16] // x0 = stackaddr, x1 = stackbase \n\
+ sub sp, x1, %[CYGTLS] // sp = stackbase - (CYGTLS) \n\
+ mov fp, xzr // clear frame pointer (x29) \n\
+ // x0 already has stackaddr \n\
+ mov x1, xzr // x1 = 0 (dwSize) \n\
+ mov x2, #0x8000 // x2 = MEM_RELEASE \n\
+ bl VirtualFree // free original stack \n\
+ mov x0, x21 // Move arg into x0 \n\
+ blr x20 // call thread function \n"
: : [WRAPPER_ARG] "r" (&wrapper_arg),
[CYGTLS] "r" (__CYGTLS_PADSIZE__)
- : "x0", "x1", "x2", "x10", "x19", "x29", "memory");
+ : "x0", "x1", "x2", "x20", "x21", "x29", "memory");
#else
#error unimplemented for this target
#endif