From: Ilya Leoshkevich <iii@linux.ibm.com>

The kernel uses orig_rax/orig_eax to store the syscall number before
a syscall. One can see this value in core dumps and ptrace.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Message-ID: <20240912093012.402366-3-iii@linux.ibm.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 linux-user/qemu.h          | 4 ++++
 linux-user/elfload.c       | 4 ++--
 linux-user/i386/cpu_loop.c | 3 +++
 3 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/linux-user/qemu.h b/linux-user/qemu.h
index 98ad848ab2..895bdd722a 100644
--- a/linux-user/qemu.h
+++ b/linux-user/qemu.h
@@ -113,6 +113,10 @@ struct TaskState {
     struct target_vm86plus_struct vm86plus;
     uint32_t v86flags;
     uint32_t v86mask;
+#endif
+#if defined(TARGET_I386)
+    /* Last syscall number. */
+    target_ulong orig_ax;
 #endif
     abi_ulong child_tidptr;
 #ifdef TARGET_M68K
diff --git a/linux-user/elfload.c b/linux-user/elfload.c
index 352960b771..6cef8db3b5 100644
--- a/linux-user/elfload.c
+++ b/linux-user/elfload.c
@@ -203,7 +203,7 @@ static void elf_core_copy_regs(target_elf_gregset_t *regs, const CPUX86State *en
     (*regs)[12] = tswapreg(env->regs[R_EDX]);
     (*regs)[13] = tswapreg(env->regs[R_ESI]);
     (*regs)[14] = tswapreg(env->regs[R_EDI]);
-    (*regs)[15] = tswapreg(env->regs[R_EAX]); /* XXX */
+    (*regs)[15] = tswapreg(get_task_state(env_cpu_const(env))->orig_ax);
     (*regs)[16] = tswapreg(env->eip);
     (*regs)[17] = tswapreg(env->segs[R_CS].selector & 0xffff);
     (*regs)[18] = tswapreg(env->eflags);
@@ -306,7 +306,7 @@ static void elf_core_copy_regs(target_elf_gregset_t *regs, const CPUX86State *en
     (*regs)[8] = tswapreg(env->segs[R_ES].selector & 0xffff);
     (*regs)[9] = tswapreg(env->segs[R_FS].selector & 0xffff);
     (*regs)[10] = tswapreg(env->segs[R_GS].selector & 0xffff);
-    (*regs)[11] = tswapreg(env->regs[R_EAX]); /* XXX */
+    (*regs)[11] = tswapreg(get_task_state(env_cpu_const(env))->orig_ax);
     (*regs)[12] = tswapreg(env->eip);
     (*regs)[13] = tswapreg(env->segs[R_CS].selector & 0xffff);
     (*regs)[14] = tswapreg(env->eflags);
diff --git a/linux-user/i386/cpu_loop.c b/linux-user/i386/cpu_loop.c
index 92beb6830c..7a35215278 100644
--- a/linux-user/i386/cpu_loop.c
+++ b/linux-user/i386/cpu_loop.c
@@ -172,6 +172,7 @@ static void emulate_vsyscall(CPUX86State *env)
     /*
      * Perform the syscall.  None of the vsyscalls should need restarting.
      */
+    get_task_state(env_cpu(env))->orig_ax = syscall;
     ret = do_syscall(env, syscall, env->regs[R_EDI], env->regs[R_ESI],
                      env->regs[R_EDX], env->regs[10], env->regs[8],
                      env->regs[9], 0, 0);
@@ -221,6 +222,7 @@ void cpu_loop(CPUX86State *env)
         case EXCP_SYSCALL:
 #endif
             /* linux syscall from int $0x80 */
+            get_task_state(cs)->orig_ax = env->regs[R_EAX];
             ret = do_syscall(env,
                              env->regs[R_EAX],
                              env->regs[R_EBX],
@@ -239,6 +241,7 @@ void cpu_loop(CPUX86State *env)
 #ifdef TARGET_X86_64
         case EXCP_SYSCALL:
             /* linux syscall from syscall instruction.  */
+            get_task_state(cs)->orig_ax = env->regs[R_EAX];
             ret = do_syscall(env,
                              env->regs[R_EAX],
                              env->regs[R_EDI],
-- 
2.43.0