This is the counterpart of the i386 feature introduced by 39a5a6a4: Add direct support for Linux kernel __fentry__ patching.
On i386, the difference between mcount and fentry is that fentry comes before the prolog. On s390 mcount already comes before the prolog, but takes 4 instructions. This patch introduces the more efficient implementation (just 1 instruction) and puts it under -mfentry flag. The produced code is compatible only with newer glibc versions, which provide the __fentry__ symbol and do not clobber %r0 when resolving lazily bound functions. Because 31-bit PLT stubs assume %r12 contains GOT address, which is not the case when the code runs before the prolog, -mfentry is allowed only for 64-bit code. Also, code compiled with -mfentry cannot be used for the nested C functions, since they both use %r0. In this case instrumentation is not insterted, and a new warning is issued for each affected nested function. * gcc/common.opt: Add the new warning. * gcc/config/s390/s390.c (s390_function_profiler): Emit "brasl %r0,__fentry__" when -mfentry is specified. (s390_option_override_internal): Disallow -mfentry for 31-bit CPUs. * gcc/config/s390/s390.opt: Add the new option. * gcc/testsuite/gcc.target/s390/mfentry-m64.c: New testcase. --- gcc/common.opt | 5 +++++ gcc/config/s390/s390.c | 18 ++++++++++++++++-- gcc/config/s390/s390.opt | 5 +++++ gcc/testsuite/gcc.target/s390/mfentry-m64.c | 8 ++++++++ 4 files changed, 34 insertions(+), 2 deletions(-) create mode 100644 gcc/testsuite/gcc.target/s390/mfentry-m64.c diff --git a/gcc/common.opt b/gcc/common.opt index c29abdb5cb1..4d031e81b09 100644 --- a/gcc/common.opt +++ b/gcc/common.opt @@ -571,6 +571,11 @@ Wattribute-alias Common Var(warn_attributes) Init(1) Warning Warn about type safety and similar errors in attribute alias and related. +Wcannot-profile +Common Var(warn_cannot_profile) Init(1) Warning +Warn when profiling instrumentation was requested, but could not be applied to +a certain function. + Wcast-align Common Var(warn_cast_align) Warning Warn about pointer casts which increase alignment. diff --git a/gcc/config/s390/s390.c b/gcc/config/s390/s390.c index 23c3f3db621..3a406b955a0 100644 --- a/gcc/config/s390/s390.c +++ b/gcc/config/s390/s390.c @@ -13144,14 +13144,22 @@ s390_function_profiler (FILE *file, int labelno) op[3] = gen_rtx_SYMBOL_REF (Pmode, label); SYMBOL_REF_FLAGS (op[3]) = SYMBOL_FLAG_LOCAL; - op[4] = gen_rtx_SYMBOL_REF (Pmode, "_mcount"); + op[4] = gen_rtx_SYMBOL_REF (Pmode, flag_fentry ? "__fentry__" : "_mcount"); if (flag_pic) { op[4] = gen_rtx_UNSPEC (Pmode, gen_rtvec (1, op[4]), UNSPEC_PLT); op[4] = gen_rtx_CONST (Pmode, op[4]); } - if (TARGET_64BIT) + if (flag_fentry) + { + if (cfun->static_chain_decl) + warning (OPT_Wcannot_profile, "nested functions cannot be profiled " + "with -mfentry on s390"); + else + output_asm_insn ("brasl\t0,%4", op); + } + else if (TARGET_64BIT) { output_asm_insn ("stg\t%0,%1", op); output_asm_insn ("larl\t%2,%3", op); @@ -15562,6 +15570,12 @@ s390_option_override_internal (bool main_args_p, /* Call target specific restore function to do post-init work. At the moment, this just sets opts->x_s390_cost_pointer. */ s390_function_specific_restore (opts, NULL); + + /* Check whether -mfentry is supported. It cannot be used in 31-bit mode, + because 31-bit PLT stubs assume that %r12 contains GOT address, which is + not the case when the code runs before the prolog. */ + if (opts->x_flag_fentry && !TARGET_64BIT) + error ("-mfentry is supported only for 64-bit CPUs"); } static void diff --git a/gcc/config/s390/s390.opt b/gcc/config/s390/s390.opt index eb16f9c821f..59e97d031b4 100644 --- a/gcc/config/s390/s390.opt +++ b/gcc/config/s390/s390.opt @@ -293,3 +293,8 @@ locations which have been patched as part of using one of the -mindirect-branch* or -mfunction-return* options. The sections consist of an array of 32 bit elements. Each entry holds the offset from the entry to the patched location. + +mfentry +Target Report Var(flag_fentry) +Emit profiling counter call at function entry before prologue. The compiled +code will require a 64-bit CPU and glibc 2.29 or newer to run. diff --git a/gcc/testsuite/gcc.target/s390/mfentry-m64.c b/gcc/testsuite/gcc.target/s390/mfentry-m64.c new file mode 100644 index 00000000000..aa3fc81248f --- /dev/null +++ b/gcc/testsuite/gcc.target/s390/mfentry-m64.c @@ -0,0 +1,8 @@ +/* { dg-do compile { target { lp64 } } } */ +/* { dg-options "-pg -mfentry" } */ + +void +profileme (void) +{ + /* { dg-final { scan-assembler "brasl\t0,__fentry__" } } */ +} -- 2.17.1