| Message ID | 1605502980-31946-1-git-send-email-yangtiezhu@loongson.cn (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [RFC] MIPS: Kconfig: Select ARCH_WANT_FRAME_POINTERS | expand |
Hello! On 16.11.2020 8:03, Tiezhu Yang wrote: > Select ARCH_WANT_FRAME_POINTERS to fix the following build error under > CONFIG_DEBUG_ATOMIC_SLEEP: > > CC arch/mips/kernel/signal.o > {standard input}: Assembler messages: > {standard input}:1775: Error: Unable to parse register name $fp > scripts/Makefile.build:283: recipe for target 'arch/mips/kernel/signal.o' failed > make[2]: *** [arch/mips/kernel/signal.o] Error 1 > scripts/Makefile.build:500: recipe for target 'arch/mips/kernel' failed > make[1]: *** [arch/mips/kernel] Error 2 > Makefile:1799: recipe for target 'arch/mips' failed > make: *** [arch/mips] Error 2 > > I think it is useful to get debugging information as described in the > following texts: > > lib/Kconfig.debug > config FRAME_POINTER > bool "Compile the kernel with frame pointers" > ... > default y if (DEBUG_INFO && UML) || ARCH_WANT_FRAME_POINTERS > help > If you say Y here the resulting kernel image will be slightly > larger and slower, but it gives very useful debugging information > in case of kernel bugs. (precise oopses/stacktraces/warnings) > > Documentation/dev-tools/kgdb.rst > This option inserts code to into the compiled executable which saves So to or into? :-) > the frame information in registers or on the stack at different points > which allows a debugger such as gdb to more accurately construct stack > back traces while debugging the kernel. > > Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn> [...] MBR, Sergei
On 11/16/2020 05:08 PM, Sergei Shtylyov wrote: > Hello! > > On 16.11.2020 8:03, Tiezhu Yang wrote: > >> Select ARCH_WANT_FRAME_POINTERS to fix the following build error under >> CONFIG_DEBUG_ATOMIC_SLEEP: >> >> CC arch/mips/kernel/signal.o >> {standard input}: Assembler messages: >> {standard input}:1775: Error: Unable to parse register name $fp >> scripts/Makefile.build:283: recipe for target >> 'arch/mips/kernel/signal.o' failed >> make[2]: *** [arch/mips/kernel/signal.o] Error 1 >> scripts/Makefile.build:500: recipe for target 'arch/mips/kernel' failed >> make[1]: *** [arch/mips/kernel] Error 2 >> Makefile:1799: recipe for target 'arch/mips' failed >> make: *** [arch/mips] Error 2 >> >> I think it is useful to get debugging information as described in the >> following texts: >> >> lib/Kconfig.debug >> config FRAME_POINTER >> bool "Compile the kernel with frame pointers" >> ... >> default y if (DEBUG_INFO && UML) || ARCH_WANT_FRAME_POINTERS >> help >> If you say Y here the resulting kernel image will be slightly >> larger and slower, but it gives very useful debugging >> information >> in case of kernel bugs. (precise oopses/stacktraces/warnings) >> >> Documentation/dev-tools/kgdb.rst >> This option inserts code to into the compiled executable which saves > > So to or into? :-) Hi Sergei, Thanks for pointing that out，this may be a typo which should be "into". I will update the commit message to correct it. Thanks, Tiezhu > >> the frame information in registers or on the stack at different points >> which allows a debugger such as gdb to more accurately construct stack >> back traces while debugging the kernel. >> >> Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn> > [...] > > MBR, Sergei
On 16.11.2020 12:47, Tiezhu Yang wrote: [...] >>> Select ARCH_WANT_FRAME_POINTERS to fix the following build error under >>> CONFIG_DEBUG_ATOMIC_SLEEP: >>> >>> CC arch/mips/kernel/signal.o >>> {standard input}: Assembler messages: >>> {standard input}:1775: Error: Unable to parse register name $fp >>> scripts/Makefile.build:283: recipe for target 'arch/mips/kernel/signal.o' >>> failed >>> make[2]: *** [arch/mips/kernel/signal.o] Error 1 >>> scripts/Makefile.build:500: recipe for target 'arch/mips/kernel' failed >>> make[1]: *** [arch/mips/kernel] Error 2 >>> Makefile:1799: recipe for target 'arch/mips' failed >>> make: *** [arch/mips] Error 2 >>> >>> I think it is useful to get debugging information as described in the >>> following texts: >>> >>> lib/Kconfig.debug >>> config FRAME_POINTER >>> bool "Compile the kernel with frame pointers" >>> ... >>> default y if (DEBUG_INFO && UML) || ARCH_WANT_FRAME_POINTERS >>> help >>> If you say Y here the resulting kernel image will be slightly >>> larger and slower, but it gives very useful debugging information >>> in case of kernel bugs. (precise oopses/stacktraces/warnings) >>> >>> Documentation/dev-tools/kgdb.rst >>> This option inserts code to into the compiled executable which saves >> >> So to or into? :-) > > Hi Sergei, > > Thanks for pointing that out，this may be a typo which should be "into". Oops, I didn't realize it was a quote from the KGDB docs... :-) > I will update the commit message to correct it. Thank you! > Thanks, > Tiezhu [...] MBR, Sergei
On Mon, 16 Nov 2020, Tiezhu Yang wrote: > Select ARCH_WANT_FRAME_POINTERS to fix the following build error under > CONFIG_DEBUG_ATOMIC_SLEEP: > > CC arch/mips/kernel/signal.o > {standard input}: Assembler messages: > {standard input}:1775: Error: Unable to parse register name $fp > scripts/Makefile.build:283: recipe for target 'arch/mips/kernel/signal.o' failed > make[2]: *** [arch/mips/kernel/signal.o] Error 1 > scripts/Makefile.build:500: recipe for target 'arch/mips/kernel' failed > make[1]: *** [arch/mips/kernel] Error 2 > Makefile:1799: recipe for target 'arch/mips' failed > make: *** [arch/mips] Error 2 Your change description does not explain to me what is going on here I am afraid, and based on it I am unable to determine if it is fit for purpose. It seems to me like your change papers over an issue by changing code generation somehow with the kernel configuration option selected so that invalid assembly is not produced anymore while invalid assembly should not happen in the first place regardless of the configuration. In particular `$fp' is a standard assembly alias for `$30' aka `$s8' and it is expected to work where `$30' or indeed any general-purpose register would: #define SYMBOLIC_REGISTER_NAMES \ [...] {"$s8", RTYPE_GP | 30}, \ {"$fp", RTYPE_GP | 30}, \ {"$ra", RTYPE_GP | 31} (from gas/config/tc-mips.c) so please show us what the assembly line GAS chokes on looks like in your case. > Documentation/dev-tools/kgdb.rst > This option inserts code to into the compiled executable which saves > the frame information in registers or on the stack at different points > which allows a debugger such as gdb to more accurately construct stack > back traces while debugging the kernel. Hmm, this is what DWARF debug information is for in the context of GDB, and I certainly used to use GDB to debug standard MIPS/Linux kernels built without the use of a separate frame pointer register (which there wasn't a kernel configuration option for back then, though which you obviously still could try to enforce with the use of `-fno-omit-frame-pointer' via CFLAGS) using JTAG probes or simulation some 15 years ago. And given the variable layout of the MIPS stack frame (unlike with some psABIs, e.g. Power) the use of `$fp' alone does not let you reconstruct a backtrace, because you cannot infer from the value of `$fp' where to retrieve the value of `$ra' from. For that you need debug information. So the information you quote seems misleading or missing the context. NB hardly any MIPS software uses the frame pointer register and all is debuggable regardless; the only actual use for $fp is `alloca', VLAs or similar dynamic frame arrangements. So what actual problem are you trying to solve, except for the assembly error, and what is your use case for `$fp' with MIPS kernel debugging? Maciej
On 11/21/2020 06:37 AM, Maciej W. Rozycki wrote: > On Mon, 16 Nov 2020, Tiezhu Yang wrote: > >> Select ARCH_WANT_FRAME_POINTERS to fix the following build error under >> CONFIG_DEBUG_ATOMIC_SLEEP: >> >> CC arch/mips/kernel/signal.o >> {standard input}: Assembler messages: >> {standard input}:1775: Error: Unable to parse register name $fp >> scripts/Makefile.build:283: recipe for target 'arch/mips/kernel/signal.o' failed >> make[2]: *** [arch/mips/kernel/signal.o] Error 1 >> scripts/Makefile.build:500: recipe for target 'arch/mips/kernel' failed >> make[1]: *** [arch/mips/kernel] Error 2 >> Makefile:1799: recipe for target 'arch/mips' failed >> make: *** [arch/mips] Error 2 > Your change description does not explain to me what is going on here I am > afraid, and based on it I am unable to determine if it is fit for purpose. > > It seems to me like your change papers over an issue by changing code > generation somehow with the kernel configuration option selected so that > invalid assembly is not produced anymore while invalid assembly should not > happen in the first place regardless of the configuration. > > In particular `$fp' is a standard assembly alias for `$30' aka `$s8' and > it is expected to work where `$30' or indeed any general-purpose register > would: > > #define SYMBOLIC_REGISTER_NAMES \ > [...] > {"$s8", RTYPE_GP | 30}, \ > {"$fp", RTYPE_GP | 30}, \ > {"$ra", RTYPE_GP | 31} > > (from gas/config/tc-mips.c) so please show us what the assembly line GAS > chokes on looks like in your case. > >> Documentation/dev-tools/kgdb.rst >> This option inserts code to into the compiled executable which saves >> the frame information in registers or on the stack at different points >> which allows a debugger such as gdb to more accurately construct stack >> back traces while debugging the kernel. > Hmm, this is what DWARF debug information is for in the context of GDB, > and I certainly used to use GDB to debug standard MIPS/Linux kernels built > without the use of a separate frame pointer register (which there wasn't a > kernel configuration option for back then, though which you obviously > still could try to enforce with the use of `-fno-omit-frame-pointer' via > CFLAGS) using JTAG probes or simulation some 15 years ago. > > And given the variable layout of the MIPS stack frame (unlike with some > psABIs, e.g. Power) the use of `$fp' alone does not let you reconstruct a > backtrace, because you cannot infer from the value of `$fp' where to > retrieve the value of `$ra' from. For that you need debug information. > > So the information you quote seems misleading or missing the context. > > NB hardly any MIPS software uses the frame pointer register and all is > debuggable regardless; the only actual use for $fp is `alloca', VLAs or > similar dynamic frame arrangements. > > So what actual problem are you trying to solve, except for the assembly > error, and what is your use case for `$fp' with MIPS kernel debugging? Hi Maciej, Thank you very much for your reply and detailed explanation. The initial aim of this patch is to fix the build error. I found this build error used with gcc 4.9.4. I try it used with gcc 7.3.1 and it has no problem. We can use new gcc version to avoid this build error. The other commit message about config and kgdb seems no related with the above build error, just give more info to discuss. As I see it now, this RFC patch is meaningless, so please ignore it and thank you again. Thanks, Tiezhu > > Maciej
diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig index ddaff19..4a4c791 100644 --- a/arch/mips/Kconfig +++ b/arch/mips/Kconfig @@ -15,6 +15,7 @@ config MIPS select ARCH_USE_QUEUED_RWLOCKS select ARCH_USE_QUEUED_SPINLOCKS select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT if MMU + select ARCH_WANT_FRAME_POINTERS select ARCH_WANT_IPC_PARSE_VERSION select BUILDTIME_TABLE_SORT select CLONE_BACKWARDS
Select ARCH_WANT_FRAME_POINTERS to fix the following build error under CONFIG_DEBUG_ATOMIC_SLEEP: CC arch/mips/kernel/signal.o {standard input}: Assembler messages: {standard input}:1775: Error: Unable to parse register name $fp scripts/Makefile.build:283: recipe for target 'arch/mips/kernel/signal.o' failed make[2]: *** [arch/mips/kernel/signal.o] Error 1 scripts/Makefile.build:500: recipe for target 'arch/mips/kernel' failed make[1]: *** [arch/mips/kernel] Error 2 Makefile:1799: recipe for target 'arch/mips' failed make: *** [arch/mips] Error 2 I think it is useful to get debugging information as described in the following texts: lib/Kconfig.debug config FRAME_POINTER bool "Compile the kernel with frame pointers" ... default y if (DEBUG_INFO && UML) || ARCH_WANT_FRAME_POINTERS help If you say Y here the resulting kernel image will be slightly larger and slower, but it gives very useful debugging information in case of kernel bugs. (precise oopses/stacktraces/warnings) Documentation/dev-tools/kgdb.rst This option inserts code to into the compiled executable which saves the frame information in registers or on the stack at different points which allows a debugger such as gdb to more accurately construct stack back traces while debugging the kernel. Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn> --- arch/mips/Kconfig | 1 + 1 file changed, 1 insertion(+)