From ecc81e33123d7ac9c11742161e128858d844b99d Mon Sep 17 00:00:00 2001 From: Andi Kleen Date: Fri, 26 Sep 2014 04:06:40 +0000 Subject: [PATCH] Add direct support for Linux kernel __fentry__ patching The Linux kernel dynamically patches in __fentry__ calls in and out at runtime. This allows using function tracing for debugging in production kernels without (significant) performance penalty. For this it needs a table pointing to each __fentry__ call. The way it is currently implemented is that a special perl script scans the object file, generates the table in a special section. When the kernel boots up it nops the calls, and then later patches in the calls again as needed. The recordmcount.pl script in the kernel works, but it seems cleaner and faster to support the code generation of the patch table directly in gcc. This also allows to nop the calls directly at code generation time, which allows to skip a patching step at kernel boot. I also expect that a patchable production tracing facility is also useful for other applications. For example it could be used in ftracer (https://github.com/andikleen/ftracer) Having a nop area at the beginning of each function can be also also useful for other things. For example it can be used to patch functions at runtime to point to different functions, to do binary updates without restarting the program (like ksplice or similar) This patch implements two new options for the i386 target: -mrecord-mcount Generate a __mcount_loc section entry for each __fentry__ or mcount call. The section is compatible with the kernel convention and the data is put into a section loaded at runtime. -mnop-mcount Generate the mcount/__fentry__ call as 5 byte nop that can be patched in later. The nop is generated as a single instruction, as the Linux kernel run time patching relies on this. Limitations: - I didn't implement -mnop-mcount for -fPIC. This would need a good single instruction 6 byte NOP and it seems a bit pointless, as the patching would prevent text sharing. - I didn't implement noping for targets that pass a variable to mcount. - The facility could be useful on architectures too. Currently the mcount code is target specific, so I made it a i386 option. gcc/: 2014-09-25 Andi Kleen * config/i386/i386.c (x86_print_call_or_nop): New function. (x86_function_profiler): Support -mnop-mcount and -mrecord-mcount. * config/i386/i386.opt (-mnop-mcount, -mrecord-mcount): Add * doc/invoke.texi: Document -mnop-mcount, -mrecord-mcount. gcc/testsuite: 2014-09-25 Andi Kleen * gcc.target/i386/nop-mcount.c: New file. * gcc.target/i386/record-mcount.c: New file. From-SVN: r215629 --- gcc/ChangeLog | 8 +++++ gcc/config/i386/i386.c | 34 ++++++++++++++++--- gcc/config/i386/i386.opt | 9 +++++ gcc/doc/invoke.texi | 17 +++++++++- gcc/testsuite/ChangeLog | 5 +++ gcc/testsuite/gcc.target/i386/nop-mcount.c | 24 +++++++++++++ gcc/testsuite/gcc.target/i386/record-mcount.c | 24 +++++++++++++ 7 files changed, 115 insertions(+), 6 deletions(-) create mode 100644 gcc/testsuite/gcc.target/i386/nop-mcount.c create mode 100644 gcc/testsuite/gcc.target/i386/record-mcount.c diff --git a/gcc/ChangeLog b/gcc/ChangeLog index e19ba1f4835..d10df70fff4 100644 --- a/gcc/ChangeLog +++ b/gcc/ChangeLog @@ -1,3 +1,11 @@ +2014-09-25 Andi Kleen + + * config/i386/i386.c (x86_print_call_or_nop): New function. + (x86_function_profiler): Support -mnop-mcount and + -mrecord-mcount. + * config/i386/i386.opt (-mnop-mcount, -mrecord-mcount): Add + * doc/invoke.texi: Document -mnop-mcount, -mrecord-mcount. + 2014-09-25 Jan Hubicka * ipa-prop.c (ipa_intraprocedural_devirtualization): Remove. diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c index 1aec70fe4ce..4cf4dea7b07 100644 --- a/gcc/config/i386/i386.c +++ b/gcc/config/i386/i386.c @@ -3975,6 +3975,13 @@ ix86_option_override_internal (bool main_args_p, } } +#ifndef NO_PROFILE_COUNTERS + if (flag_nop_mcount) + error ("-mnop-mcount is not compatible with this target"); +#endif + if (flag_nop_mcount && flag_pic) + error ("-mnop-mcount is not implemented for -fPIC"); + /* Accept -msseregparm only if at least SSE support is enabled. */ if (TARGET_SSEREGPARM_P (opts->x_target_flags) && ! TARGET_SSE_P (opts->x_ix86_isa_flags)) @@ -39040,6 +39047,17 @@ x86_field_alignment (tree field, int computed) return computed; } +/* Print call to TARGET to FILE. */ + +static void +x86_print_call_or_nop (FILE *file, const char *target) +{ + if (flag_nop_mcount) + fprintf (file, "1:\tnopl 0x00(%%eax,%%eax,1)\n"); /* 5 byte nop. */ + else + fprintf (file, "1:\tcall\t%s\n", target); +} + /* Output assembler code to FILE to increment profiler label # LABELNO for profiling a function entry. */ void @@ -39047,7 +39065,6 @@ x86_function_profiler (FILE *file, int labelno ATTRIBUTE_UNUSED) { const char *mcount_name = (flag_fentry ? MCOUNT_NAME_BEFORE_PROLOGUE : MCOUNT_NAME); - if (TARGET_64BIT) { #ifndef NO_PROFILE_COUNTERS @@ -39055,9 +39072,9 @@ x86_function_profiler (FILE *file, int labelno ATTRIBUTE_UNUSED) #endif if (!TARGET_PECOFF && flag_pic) - fprintf (file, "\tcall\t*%s@GOTPCREL(%%rip)\n", mcount_name); + fprintf (file, "1:\tcall\t*%s@GOTPCREL(%%rip)\n", mcount_name); else - fprintf (file, "\tcall\t%s\n", mcount_name); + x86_print_call_or_nop (file, mcount_name); } else if (flag_pic) { @@ -39065,7 +39082,7 @@ x86_function_profiler (FILE *file, int labelno ATTRIBUTE_UNUSED) fprintf (file, "\tleal\t%sP%d@GOTOFF(%%ebx),%%" PROFILE_COUNT_REGISTER "\n", LPREFIX, labelno); #endif - fprintf (file, "\tcall\t*%s@GOT(%%ebx)\n", mcount_name); + fprintf (file, "1:\tcall\t*%s@GOT(%%ebx)\n", mcount_name); } else { @@ -39073,7 +39090,14 @@ x86_function_profiler (FILE *file, int labelno ATTRIBUTE_UNUSED) fprintf (file, "\tmovl\t$%sP%d,%%" PROFILE_COUNT_REGISTER "\n", LPREFIX, labelno); #endif - fprintf (file, "\tcall\t%s\n", mcount_name); + x86_print_call_or_nop (file, mcount_name); + } + + if (flag_record_mcount) + { + fprintf (file, "\t.section __mcount_loc, \"a\",@progbits\n"); + fprintf (file, "\t.%s 1b\n", TARGET_64BIT ? "quad" : "long"); + fprintf (file, "\t.previous\n"); } } diff --git a/gcc/config/i386/i386.opt b/gcc/config/i386/i386.opt index 9208b766030..acf6b375157 100644 --- a/gcc/config/i386/i386.opt +++ b/gcc/config/i386/i386.opt @@ -789,6 +789,15 @@ mfentry Target Report Var(flag_fentry) Init(-1) Emit profiling counter call at function entry before prologue. +mrecord-mcount +Target Report Var(flag_record_mcount) Init(0) +Generate __mcount_loc section with all mcount or __fentry__ calls. + +mnop-mcount +Target Report Var(flag_nop_mcount) Init(0) +Generate mcount/__fentry__ calls as nops. To activate they need to be +patched in. + m8bit-idiv Target Report Mask(USE_8BIT_IDIV) Save Expand 32bit/64bit integer divide into 8bit unsigned integer divide with run-time check diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi index eae4ab1ac5e..0c3f4beaea9 100644 --- a/gcc/doc/invoke.texi +++ b/gcc/doc/invoke.texi @@ -692,7 +692,7 @@ Objective-C and Objective-C++ Dialects}. -momit-leaf-frame-pointer -mno-red-zone -mno-tls-direct-seg-refs @gol -mcmodel=@var{code-model} -mabi=@var{name} -maddress-mode=@var{mode} @gol -m32 -m64 -mx32 -m16 -mlarge-data-threshold=@var{num} @gol --msse2avx -mfentry -m8bit-idiv @gol +-msse2avx -mfentry -mrecord-mcount -mnop-mcount -m8bit-idiv @gol -mavx256-split-unaligned-load -mavx256-split-unaligned-store @gol -mstack-protector-guard=@var{guard}} @@ -15988,6 +15988,21 @@ counter call before the prologue. Note: On x86 architectures the attribute @code{ms_hook_prologue} isn't possible at the moment for @option{-mfentry} and @option{-pg}. +@item -mrecord-mcount +@itemx -mno-record-mcount +@opindex mrecord-mcount +If profiling is active (@option{-pg}), generate a __mcount_loc section +that contains pointers to each profiling call. This is useful for +automatically patching and out calls. + +@item -mnop-mcount +@itemx -mno-nop-mcount +@opindex mnop-mcount +If profiling is active (@option{-pg}), generate the calls to +the profiling functions as nops. This is useful when they +should be patched in later dynamically. This is likely only +useful together with @option{-mrecord-mcount}. + @item -m8bit-idiv @itemx -mno-8bit-idiv @opindex 8bit-idiv diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog index f9e2445f26b..0074c0c09a0 100644 --- a/gcc/testsuite/ChangeLog +++ b/gcc/testsuite/ChangeLog @@ -1,3 +1,8 @@ +2014-09-25 Andi Kleen + + * gcc.target/i386/nop-mcount.c: New file. + * gcc.target/i386/record-mcount.c: New file. + 2014-09-25 Sandra Loosemore * gcc.dg/vect/pr56933.c: Don't specify "dg-do run" explicitly. diff --git a/gcc/testsuite/gcc.target/i386/nop-mcount.c b/gcc/testsuite/gcc.target/i386/nop-mcount.c new file mode 100644 index 00000000000..25922315604 --- /dev/null +++ b/gcc/testsuite/gcc.target/i386/nop-mcount.c @@ -0,0 +1,24 @@ +/* Test -mnop-mcount */ +/* { dg-do compile } */ +/* { dg-options "-pg -mfentry -mrecord-mcount -mnop-mcount" } */ +/* { dg-final { scan-assembler-not "__fentry__" } } */ +/* Origin: Andi Kleen */ +extern void foobar(char *); + +void func(void) +{ + foobar ("Hello world\n"); +} + +void func2(void) +{ + int i; + for (i = 0; i < 10; i++) + foobar ("Hello world"); +} + +void func3(a) +char *a; +{ + foobar("Hello world"); +} diff --git a/gcc/testsuite/gcc.target/i386/record-mcount.c b/gcc/testsuite/gcc.target/i386/record-mcount.c new file mode 100644 index 00000000000..dae413e9b0e --- /dev/null +++ b/gcc/testsuite/gcc.target/i386/record-mcount.c @@ -0,0 +1,24 @@ +/* Test -mrecord-mcount */ +/* { dg-do compile } */ +/* { dg-options "-pg -mrecord-mcount" } */ +/* { dg-final { scan-assembler "mcount_loc" } } */ +/* Origin: Andi Kleen */ +extern void foobar(char *); + +void func(void) +{ + foobar ("Hello world\n"); +} + +void func2(void) +{ + int i; + for (i = 0; i < 10; i++) + foobar ("Hello world"); +} + +void func3(a) +char *a; +{ + foobar("Hello world"); +} -- 2.30.2