Messages in this thread Patch in this message | | | Subject | Re: [PATCH] ARM: Remove the special printing format of pc and lr in __show_regs() | From | "Leizhen (ThunderTown)" <> | Date | Tue, 9 Aug 2022 17:03:56 +0800 |
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On 2022/8/9 10:09, Leizhen (ThunderTown) wrote: > > > On 2022/8/8 17:41, Russell King (Oracle) wrote: >> On Mon, Aug 01, 2022 at 11:20:16AM +0800, Zhen Lei wrote: >>> Currently, instruction pointers are printed in [<%08lx>] format to make >>> them more visible. However, it is not necessary in __show_regs() because >>> they have the prefix 'pc :' or 'lr :', and it is also inconsistent with >>> that of other registers, which causes misalignment. >> >> The formatting is not "to make them more visible" - it was to mark the >> addresses that we wanted the ksymoops utility to translate to kernel >> symbols before we had kallsyms in the kernel. If one disables kallsyms, >> then we still need a way to translate kernel addresses to symbols. > > I searched the git log and found that the ksymoops utility is discarded. > > See: > 073a9ecb3a73401662430bb955aedeac1de643d1 > However, a commit in the pre-git era [1] had added the statement, > "ksymoops is useless on 2.6. Please use the Oops in its original format". > > That statement existed until commit 4eb9241127a0 ("Documentation: > admin-guide: update bug-hunting.rst") finally removed the stale > ksymoops information. > > 4eb9241127a0b5ac3aaaf1b246728009527ebc86 > - delete all references to ksymoops since it is no longer applicable; > >> >> I notice there is a script which helps with this that is part of the >> kernel source - scripts/decode_stacktrace.sh. I haven't tried this on >> arm32 since I always use kallsyms - and I suspect that is rather >> universally true as it avoids needing System.map files etc to decode >> the oops. That said, if you're building a kernel for small systems, >> you probably don't want the overhead of kallsyms.
Hi, Russell:
I re-examined the code and found that 'pc' and 'lr' had extra printing in __show_regs(). Therefore, maybe v2 should be changed as follows, as is done in dump_backtrace_entry():
diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c index 96f3fbd51764292..2b0b49821cbf2f5 100644 --- a/arch/arm/kernel/process.c +++ b/arch/arm/kernel/process.c @@ -134,9 +134,15 @@ void __show_regs(struct pt_regs *regs)
show_regs_print_info(KERN_DEFAULT);
+#ifndef CONFIG_KALLSYMS + printk("PC is at [<%08lx>]\n", instruction_pointer(regs)); + printk("LR is at [<%08lx>]\n", regs->ARM_lr); +#else printk("PC is at %pS\n", (void *)instruction_pointer(regs)); printk("LR is at %pS\n", (void *)regs->ARM_lr); - printk("pc : [<%08lx>] lr : [<%08lx>] psr: %08lx\n", +#endif + + printk("pc : %08lx lr : %08lx psr: %08lx\n", regs->ARM_pc, regs->ARM_lr, regs->ARM_cpsr); printk("sp : %08lx ip : %08lx fp : %08lx\n", regs->ARM_sp, regs->ARM_ip, regs->ARM_fp);
So that there are no concerns that you mentioned.
CONFIG_KALLSYMS=n: PC is at [<801993d4>] LR is at [<801993d4>] pc : 801993d4 lr : 801993d4 psr: 60000013 sp : c49f9f28 ip : 00000001 fp : 00000001 CONFIG_KALLSYMS=y: PC is at ktime_get+0x4c/0xe8 LR is at ktime_get+0x4c/0xe8 pc : 8019a4ac lr : 8019a4ac psr: 60000013 sp : c49f9f28 ip : 00000001 fp : 00000001
> > Yes, I read scripts/decode_stacktrace.sh, it requires the format "[<...>]". > But if that's the only concern, maybe we can do the conversion from > "pc: addr" and "lr: addr" to "[<addr>]" first in scripts/decode_stacktrace.sh > > I'm usually "objdump -d vmlinux > asm_file", then search "addr:" in asm_file. > > Honestly, I think format "[<...>]" is dump_backtrace()'s requirement, not __show_regs()'s. > > >> >> So, there's an argument for keeping it - it's an API in that it >> provides hints to scripting to identify which values need to be >> converted to symbols. There's also the argument for getting rid of it, >> which is that hardly anyone does that anymore. >> >> The question is, which is the more important argument, and I don't >> think there's a definite answer. So I'm inclined to leave this >> as-is. > > OK > >> >
-- Regards, Zhen Lei
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