Re: [PATCH v2 3/5] gdbstub: Save target's siginfo

[Richard Henderson]

On 3/7/24 08:26, Gustavo Romero wrote:
Save target's siginfo into gdbserver_state so it can be used later, for
example, in any stub that requires the target's si_signo and si_code.
This change affects only linux-user mode.

Signed-off-by: Gustavo Romero <gustavo.rom...@linaro.org>
Suggested-by: Richard Henderson <richard.hender...@linaro.org>
---
  gdbstub/internals.h    |  3 +++
  gdbstub/user-target.c  |  3 ++-
  gdbstub/user.c         | 14 ++++++++++----
  include/gdbstub/user.h |  6 +++++-
  linux-user/main.c      |  2 +-
  linux-user/signal.c    |  5 ++++-
  6 files changed, 25 insertions(+), 8 deletions(-)

diff --git a/gdbstub/internals.h b/gdbstub/internals.h
index 56b7c13b75..a7cc69dab3 100644
--- a/gdbstub/internals.h
+++ b/gdbstub/internals.h
@@ -58,6 +58,9 @@ typedef struct GDBState {
      int line_csum; /* checksum at the end of the packet */
      GByteArray *last_packet;
      int signal;
+#ifdef CONFIG_USER_ONLY
+    uint8_t siginfo[MAX_SIGINFO_LENGTH];
+#endif

If we this in GDBUserState in user.c -- no need for ifdefs then.

--- a/gdbstub/user-target.c
+++ b/gdbstub/user-target.c
@@ -10,11 +10,12 @@
  #include "qemu/osdep.h"
  #include "exec/gdbstub.h"
  #include "qemu.h"
-#include "internals.h"
  #ifdef CONFIG_LINUX
  #include "linux-user/loader.h"
  #include "linux-user/qemu.h"
+#include "gdbstub/user.h"
  #endif
+#include "internals.h"
  
  /*
   * Map target signal numbers to GDB protocol signal numbers and vice

Why are any changes required here?
Perhaps this is improper patch split from one of the others?

@@ -140,6 +141,11 @@ int gdb_handlesig(CPUState *cpu, int sig, const char 
*reason)
          return sig;
      }
  
+    if (siginfo) {
+        /* Save target-specific siginfo. */
+        memcpy(gdbserver_state.siginfo, siginfo, siginfo_len);
+    }

A comment here about asserting the size at compile-time elsewhere would be welcome for 
future code browsers.

Need to record siginfo_len for later use -- you don't want to expose all 128 bytes if the 
actual structure is smaller.

@@ -510,7 +516,7 @@ void gdb_breakpoint_remove_all(CPUState *cs)
  void gdb_syscall_handling(const char *syscall_packet)
  {
      gdb_put_packet(syscall_packet);
-    gdb_handlesig(gdbserver_state.c_cpu, 0, NULL);
+    gdb_handlesig(gdbserver_state.c_cpu, 0, NULL, NULL, 0);
  }
  
  static bool should_catch_syscall(int num)
@@ -528,7 +534,7 @@ void gdb_syscall_entry(CPUState *cs, int num)
  {
      if (should_catch_syscall(num)) {
          g_autofree char *reason = g_strdup_printf("syscall_entry:%x;", num);
-        gdb_handlesig(cs, gdb_target_sigtrap(), reason);
+        gdb_handlesig(cs, gdb_target_sigtrap(), reason, NULL, 0);
      }
  }
  
@@ -536,7 +542,7 @@ void gdb_syscall_return(CPUState *cs, int num)
  {
      if (should_catch_syscall(num)) {
          g_autofree char *reason = g_strdup_printf("syscall_return:%x;", num);
-        gdb_handlesig(cs, gdb_target_sigtrap(), reason);
+        gdb_handlesig(cs, gdb_target_sigtrap(), reason, NULL, 0);
      }

All of this makes me wonder if we should provide a different interface for syscalls, even 
if it uses the same code paths internally.

Do we want to zero the gdbserver siginfo to indicate that the contents are no longer 
valid?  I know it's not a real signal delivered to the process, but might we need to 
construct a simple siginfo struct to match the sigtrap?


r~