Fix issue #15778: GDB Aarch64 signal frame unwinder issue

The root cause of this issue is unwinder of "#3 <signal handler called>" doesn't supply right values of registers. When GDB want to get the previous frame of "#3 <signal handler called>", it will call cache init function of unwinder "aarch64_linux_sigframe_init". The address or the value of the registers is get from this function. So the bug is inside thie function. I check the asm code of "#3 <signal handler called>": (gdb) frame 3 (gdb) p $pc $1 = (void (*)()) 0x7f931fa4d0 (gdb) disassemble $pc, +10 Dump of assembler code from 0x7f931fa4d0 to 0x7f931fa4da: => 0x0000007f931fa4d0: mov x8, #0x8b // #139 0x0000007f931fa4d4: svc #0x0 0x0000007f931fa4d8: nop This is the syscall sys_rt_sigreturn, Linux kernel function "restore_sigframe" will set the frame: for (i = 0; i < 31; i++) __get_user_error(regs->regs[i], &sf->uc.uc_mcontext.regs[i], err); __get_user_error(regs->sp, &sf->uc.uc_mcontext.sp, err); __get_user_error(regs->pc, &sf->uc.uc_mcontext.pc, err); The struct of uc_mcontext is: struct sigcontext { __u64 fault_address; /* AArch64 registers */ __u64 regs[31]; __u64 sp; __u64 pc; __u64 pstate; /* 4K reserved for FP/SIMD state and future expansion */ __u8 __reserved[4096] __attribute__((__aligned__(16))); }; But in GDB function "aarch64_linux_sigframe_init", the code the get address of registers is: for (i = 0; i < 31; i++) { trad_frame_set_reg_addr (this_cache, AARCH64_X0_REGNUM + i, sigcontext_addr + AARCH64_SIGCONTEXT_XO_OFFSET + i * AARCH64_SIGCONTEXT_REG_SIZE); } trad_frame_set_reg_addr (this_cache, AARCH64_FP_REGNUM, fp); trad_frame_set_reg_addr (this_cache, AARCH64_LR_REGNUM, fp + 8); trad_frame_set_reg_addr (this_cache, AARCH64_PC_REGNUM, fp + 8); The code that get pc and sp is not right, so I change the code according to Linux kernel code: trad_frame_set_reg_addr (this_cache, AARCH64_SP_REGNUM, sigcontext_addr + AARCH64_SIGCONTEXT_XO_OFFSET + 31 * AARCH64_SIGCONTEXT_REG_SIZE); trad_frame_set_reg_addr (this_cache, AARCH64_PC_REGNUM, sigcontext_addr + AARCH64_SIGCONTEXT_XO_OFFSET + 32 * AARCH64_SIGCONTEXT_REG_SIZE); The issue was fixed by this change, and I did the regression test. It also fixed a lot of other XFAIL and FAIL. 2014-05-20 Hui Zhu <[email protected]> Yao Qi <[email protected]> PR backtrace/16558 * aarch64-linux-tdep.c (aarch64_linux_sigframe_init): Update comments and change address of sp and pc.
xdje42 · May 20, 2014 · f2205de · f2205de
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commit f2205de
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Showing 2 changed files with 41 additions and 29 deletions.
diff --git a/gdb/ChangeLog b/gdb/ChangeLog
@@ -1,3 +1,10 @@
+2014-05-20  Hui Zhu  <[email protected]>
+	    Yao Qi  <[email protected]>
+
+	PR backtrace/16558
+	* aarch64-linux-tdep.c (aarch64_linux_sigframe_init): Update comments
+	and change address of sp and pc.
+
 2014-05-19  Tom Tromey  <[email protected]>
 
 	* gdbtypes.c (rank_function): Use XNEWVEC.

diff --git a/gdb/aarch64-linux-tdep.c b/gdb/aarch64-linux-tdep.c
@@ -53,28 +53,30 @@
 
 /* Signal frame handling.
 
-      +----------+  ^
-      | saved lr |  |
-   +->| saved fp |--+
-   |  |          |
-   |  |          |
-   |  +----------+
-   |  | saved lr |
-   +--| saved fp |
-   ^  |          |
-   |  |          |
-   |  +----------+
-   ^  |          |
-   |  | signal   |
-   |  |          |
-   |  | saved lr |-->interrupted_function_pc
-   +--| saved fp |
-   |  +----------+
-   |  | saved lr |--> default_restorer (movz x8, NR_sys_rt_sigreturn; svc 0)
-   +--| saved fp |<- FP
-      |          |
-      |          |<- SP
-      +----------+
+      +------------+  ^
+      | saved lr   |  |
+   +->| saved fp   |--+
+   |  |            |
+   |  |            |
+   |  +------------+
+   |  | saved lr   |
+   +--| saved fp   |
+   ^  |            |
+   |  |            |
+   |  +------------+
+   ^  |            |
+   |  | signal     |
+   |  |            |        SIGTRAMP_FRAME (struct rt_sigframe)
+   |  | saved regs |
+   +--| saved sp   |--> interrupted_sp
+   |  | saved pc   |--> interrupted_pc
+   |  |            |
+   |  +------------+
+   |  | saved lr   |--> default_restorer (movz x8, NR_sys_rt_sigreturn; svc 0)
+   +--| saved fp   |<- FP
+      |            |         NORMAL_FRAME
+      |            |<- SP
+      +------------+
 
   On signal delivery, the kernel will create a signal handler stack
   frame and setup the return address in LR to point at restorer stub.
@@ -123,6 +125,8 @@
   d28015a8        movz    x8, #0xad
   d4000001        svc     #0x0
 
+  This is a system call sys_rt_sigreturn.
+
   We detect signal frames by snooping the return code for the restorer
   instruction sequence.
 
@@ -146,7 +150,6 @@ aarch64_linux_sigframe_init (const struct tramp_frame *self,
 {
   struct gdbarch *gdbarch = get_frame_arch (this_frame);
   CORE_ADDR sp = get_frame_register_unsigned (this_frame, AARCH64_SP_REGNUM);
-  CORE_ADDR fp = get_frame_register_unsigned (this_frame, AARCH64_FP_REGNUM);
   CORE_ADDR sigcontext_addr =
     sp
     + AARCH64_RT_SIGFRAME_UCONTEXT_OFFSET
@@ -160,12 +163,14 @@ aarch64_linux_sigframe_init (const struct tramp_frame *self,
 			       sigcontext_addr + AARCH64_SIGCONTEXT_XO_OFFSET
 			       + i * AARCH64_SIGCONTEXT_REG_SIZE);
     }
-
-  trad_frame_set_reg_addr (this_cache, AARCH64_FP_REGNUM, fp);
-  trad_frame_set_reg_addr (this_cache, AARCH64_LR_REGNUM, fp + 8);
-  trad_frame_set_reg_addr (this_cache, AARCH64_PC_REGNUM, fp + 8);
-
-  trad_frame_set_id (this_cache, frame_id_build (fp, func));
+  trad_frame_set_reg_addr (this_cache, AARCH64_SP_REGNUM,
+			   sigcontext_addr + AARCH64_SIGCONTEXT_XO_OFFSET
+			     + 31 * AARCH64_SIGCONTEXT_REG_SIZE);
+  trad_frame_set_reg_addr (this_cache, AARCH64_PC_REGNUM,
+			   sigcontext_addr + AARCH64_SIGCONTEXT_XO_OFFSET
+			     + 32 * AARCH64_SIGCONTEXT_REG_SIZE);
+
+  trad_frame_set_id (this_cache, frame_id_build (sp, func));
 }
 
 static const struct tramp_frame aarch64_linux_rt_sigframe =