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linux-user/arm: Deliver SIGTRAP for UDF patterns used as breakpoints

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The Linux kernel doesn't use the official bkpt insn for breakpoints;
instead it uses three instructions in the guaranteed-to-UNDEF space,
and generates SIGTRAP for these rather than the SIGILL that most
UNDEF insns generate:

https://elixir.bootlin.com/linux/v5.9.8/source/arch/arm/kernel/ptrace.c#L197

Make QEMU treat these insns specially too.  The main benefit of this
is that if you're running a debugger on a guest program that runs
into a GCC __builtin_trap() or LLVM "trap because execution should
never reach here" then you'll get the expected signal rather than a
SIGILL.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20201117155634.6924-1-peter.maydell@linaro.org
This commit is contained in:
Peter Maydell 2020-11-17 15:56:34 +00:00
parent 6951595183
commit acebed948c
1 changed files with 28 additions and 0 deletions
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28
linux-user/arm/cpu_loop.c
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@ -205,6 +205,24 @@ do_kernel_trap(CPUARMState *env)
return 0;
}
static bool insn_is_linux_bkpt(uint32_t opcode, bool is_thumb)
{
/*
* Return true if this insn is one of the three magic UDF insns
* which the kernel treats as breakpoint insns.
*/
if (!is_thumb) {
return (opcode & 0x0fffffff) == 0x07f001f0;
} else {
/*
* Note that we get the two halves of the 32-bit T32 insn
* in the opposite order to the value the kernel uses in
* its undef_hook struct.
*/
return ((opcode & 0xffff) == 0xde01) || (opcode == 0xa000f7f0);
}
}
void cpu_loop(CPUARMState *env)
{
CPUState *cs = env_cpu(env);
@ -234,6 +252,16 @@ void cpu_loop(CPUARMState *env)
/* FIXME - what to do if get_user() fails? */
get_user_code_u32(opcode, env->regs[15], env);
/*
* The Linux kernel treats some UDF patterns specially
* to use as breakpoints (instead of the architectural
* bkpt insn). These should trigger a SIGTRAP rather
* than SIGILL.
*/
if (insn_is_linux_bkpt(opcode, env->thumb)) {
goto excp_debug;
}
rc = EmulateAll(opcode, &ts->fpa, env);
if (rc == 0) { /* illegal instruction */
info.si_signo = TARGET_SIGILL;