From 2a83afe72a2b5760155c2dd840c776aee292dc90 Mon Sep 17 00:00:00 2001 From: Michael Ellerman Date: Tue, 31 May 2022 16:59:36 +1000 Subject: powerpc/64: Drop ppc_inst_as_str() The ppc_inst_as_str() macro tries to make printing variable length, aka "prefixed", instructions convenient. It mostly succeeds, but it does hide an on-stack buffer, which triggers stack protector. More problematically it doesn't compile at all with GCC 12, with -Wdangling-pointer, due to the fact that it returns the char buffer declared inside the macro: arch/powerpc/kernel/trace/ftrace.c: In function '__ftrace_modify_call': ./include/linux/printk.h:475:44: error: using a dangling pointer to '__str' [-Werror=dangling-pointer=] 475 | #define printk(fmt, ...) printk_index_wrap(_printk, fmt, ##__VA_ARGS__) ... arch/powerpc/kernel/trace/ftrace.c:567:17: note: in expansion of macro 'pr_err' 567 | pr_err("Not expected bl: opcode is %s\n", ppc_inst_as_str(op)); | ^~~~~~ ./arch/powerpc/include/asm/inst.h:156:14: note: '__str' declared here 156 | char __str[PPC_INST_STR_LEN]; \ | ^~~~~ This could be fixed by having the caller declare the buffer, but in some places there'd need to be two buffers. In all cases where ppc_inst_as_str() is used the output is not really meant for user consumption, it's almost always indicative of a kernel bug. A simpler solution is to just print the value as an unsigned long. For normal instructions the output is identical. For prefixed instructions the value is printed as a single 64-bit quantity, whereas previously the low half was printed first. But that is good enough for debug output, especially as prefixed instructions will be rare in kernel code in practice. Old: c000000000111170 60420000 ori r2,r2,0 c000000000111174 04100001 e580fb00 .long 0xe580fb0004100001 New: c00000000010f90c 60420000 ori r2,r2,0 c00000000010f910 e580fb0004100001 .long 0xe580fb0004100001 Reported-by: Bagas Sanjaya Reported-by: Petr Mladek Signed-off-by: Michael Ellerman Tested-by: Bagas Sanjaya Link: https://lore.kernel.org/r/20220531065936.3674348-1-mpe@ellerman.id.au --- arch/powerpc/lib/test_emulate_step.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) (limited to 'arch/powerpc/lib') diff --git a/arch/powerpc/lib/test_emulate_step.c b/arch/powerpc/lib/test_emulate_step.c index 4f141daafcff..f2e47be05e8c 100644 --- a/arch/powerpc/lib/test_emulate_step.c +++ b/arch/powerpc/lib/test_emulate_step.c @@ -1616,11 +1616,11 @@ static int __init emulate_compute_instr(struct pt_regs *regs, if (analysed != 1 || GETTYPE(op.type) != COMPUTE) { if (negative) return -EFAULT; - pr_info("emulation failed, instruction = %s\n", ppc_inst_as_str(instr)); + pr_info("emulation failed, instruction = %08lx\n", ppc_inst_as_ulong(instr)); return -EFAULT; } if (analysed == 1 && negative) - pr_info("negative test failed, instruction = %s\n", ppc_inst_as_str(instr)); + pr_info("negative test failed, instruction = %08lx\n", ppc_inst_as_ulong(instr)); if (!negative) emulate_update_regs(regs, &op); return 0; @@ -1637,7 +1637,7 @@ static int __init execute_compute_instr(struct pt_regs *regs, /* Patch the NOP with the actual instruction */ patch_instruction_site(&patch__exec_instr, instr); if (exec_instr(regs)) { - pr_info("execution failed, instruction = %s\n", ppc_inst_as_str(instr)); + pr_info("execution failed, instruction = %08lx\n", ppc_inst_as_ulong(instr)); return -EFAULT; } -- cgit v1.2.3