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
