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AArch64: Detect exit from execve syscall 

Checking the syscall number when stopped on entry/exit relies on checking
the value in register X8.

However, on exit from an execve syscall, the registers will all be cleared.
Given this is only checked on syscall entry/exit, then a cleared register
state either means execve exit or syscall 0 (io_setup) entry with invalid
parameters and an invalid FR and LR, which in reality should never happen.
Use this to detect execve exit.

Move function to allow use of aarch64_sys_execve enum, and use newer
regcache functions.

Fixes gdb.base/catch-syscall.exp on Aarch64.

gdb/ChangeLog:

	* aarch64-linux-tdep.c (aarch64_linux_get_syscall_number): Check
	for execve.
This commit is contained in:
Alan Hayward 2019-02-11 16:38:29 +00:00
parent 7115ab9c4b
commit ea638c4312
2 changed files with 39 additions and 22 deletions
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5
gdb/ChangeLog
View File

@ -1,3 +1,8 @@
2019-02-11 Alan Hayward <alan.hayward@arm.com>
* aarch64-linux-tdep.c (aarch64_linux_get_syscall_number): Check
for execve.
2019-02-10 Philippe Waroquiers <philippe.waroquiers@skynet.be>
* c-exp.y (direct_abs_decl): Use emplace_back to record the

56
gdb/aarch64-linux-tdep.c
View File

@ -757,28 +757,6 @@ aarch64_stap_parse_special_token (struct gdbarch *gdbarch,
return 1;
}
/* Implement the "get_syscall_number" gdbarch method. */
static LONGEST
aarch64_linux_get_syscall_number (struct gdbarch *gdbarch,
thread_info *thread)
{
struct regcache *regs = get_thread_regcache (thread);
enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
/* The content of register x8. */
gdb_byte buf[X_REGISTER_SIZE];
/* The result. */
LONGEST ret;
/* Getting the system call number from the register x8. */
regs->cooked_read (AARCH64_DWARF_X0 + 8, buf);
ret = extract_signed_integer (buf, X_REGISTER_SIZE, byte_order);
return ret;
}
/* AArch64 process record-replay constructs: syscall, signal etc. */
struct linux_record_tdep aarch64_linux_record_tdep;
@ -1334,6 +1312,40 @@ aarch64_canonicalize_syscall (enum aarch64_syscall syscall_number)
}
}
/* Retrieve the syscall number at a ptrace syscall-stop, either on syscall entry
or exit. Return -1 upon error. */
static LONGEST
aarch64_linux_get_syscall_number (struct gdbarch *gdbarch, thread_info *thread)
{
struct regcache *regs = get_thread_regcache (thread);
LONGEST ret;
/* Get the system call number from register x8. */
regs->cooked_read (AARCH64_X0_REGNUM + 8, &ret);
/* On exit from a successful execve, we will be in a new process and all the
registers will be cleared - x0 to x30 will be 0, except for a 1 in x7.
This function will only ever get called when stopped at the entry or exit
of a syscall, so by checking for 0 in x0 (arg0/retval), x1 (arg1), x8
(syscall), x29 (FP) and x30 (LR) we can infer:
1) Either inferior is at exit from sucessful execve.
2) Or inferior is at entry to a call to io_setup with invalid arguments and
a corrupted FP and LR.
It should be safe enough to assume case 1. */
if (ret == 0)
{
LONGEST x1 = -1, fp = -1, lr = -1;
regs->cooked_read (AARCH64_X0_REGNUM + 1, &x1);
regs->cooked_read (AARCH64_FP_REGNUM, &fp);
regs->cooked_read (AARCH64_LR_REGNUM, &lr);
if (x1 == 0 && fp ==0 && lr == 0)
return aarch64_sys_execve;
}
return ret;
}
/* Record all registers but PC register for process-record. */
static int