Cherry picked from glibc-2.42
0d99714680 * hurd: Clear FP exceptions before calling signal handler
From 0d9971468087c77e8727638123ae4aa60724e0ff Mon Sep 17 00:00:00 2001
From: Samuel Thibault <samuel.thibault@ens-lyon.org>
Date: Mon, 21 Apr 2025 19:58:04 +0200
Subject: [PATCH] hurd: Clear FP exceptions before calling signal handler
This avoids SIGFPE handlers (or code longjmp-ed to) getting disturbed by the
exception that generated it.
Note: gcc's unwinding depends on the rpc_wait_trampoline/trampoline exact
code, so we here avoid breaking it.
---
sysdeps/mach/hurd/x86/trampoline.c | 14 ++++++++++----
1 file changed, 10 insertions(+), 4 deletions(-)
diff --git a/sysdeps/mach/hurd/x86/trampoline.c b/sysdeps/mach/hurd/x86/trampoline.c
index 02510b178c..6f23c567da 100644
--- a/sysdeps/mach/hurd/x86/trampoline.c
+++ b/sysdeps/mach/hurd/x86/trampoline.c
@@ -461,7 +461,10 @@ _hurd_setup_sighandler (struct hurd_sigstate *ss, const struct sigaction *action
- in gdb: gdb/i386-gnu-tdep.c gnu_sigtramp_code. */
#ifdef __x86_64__
-asm ("rpc_wait_trampoline:\n"
+asm ("trampoline:\n"
+ "fnclex\n" /* Clear any pending exception. */
+ "jmp _trampoline\n"
+ "rpc_wait_trampoline:\n"
/* This is the entry point when we have an RPC reply message to receive
before running the handler. The MACH_MSG_SEND bit has already been
cleared in the OPTION argument in our %rsi. The interrupted user
@@ -480,7 +483,7 @@ asm ("rpc_wait_trampoline:\n"
/* Switch to the signal stack. */
"movq %rbx, %rsp\n"
- "trampoline:\n"
+ "_trampoline:\n"
/* Entry point for running the handler normally. The arguments to the
handler function are on the top of the stack, same as in the i386
version:
@@ -506,7 +509,10 @@ asm ("rpc_wait_trampoline:\n"
"movq 16(%rsp), %rdi\n"
"ret");
#else
-asm ("rpc_wait_trampoline:\n");
+asm ("trampoline:\n"
+ "fnclex\n" /* Clear any pending exception. */
+ "jmp _trampoline\n"
+ "rpc_wait_trampoline:\n");
/* This is the entry point when we have an RPC reply message to receive
before running the handler. The MACH_MSG_SEND bit has already been
cleared in the OPTION argument on our stack. The interrupted user
@@ -526,7 +532,7 @@ asm (/* Retry the interrupted mach_msg system call. */
/* Switch to the signal stack. */
"movl %ebx, %esp\n");
- asm ("trampoline:\n");
+asm ("_trampoline:\n");
/* Entry point for running the handler normally. The arguments to the
handler function are already on the top of the stack:
--
2.51.0