We'd like to introduce a new codegen option to align with the old
"-Wa,-mla-global-with-pcrel" and avoid a performance & size regression
building the Linux kernel with new-reloc toolchain. And it should be
also useful for building statically linked executables, firmwares (EDK2
for example), and other OS kernels.
OK for trunk?
-- >8 --
As a new target, LoongArch does not use copy relocation as it's
problematic in some circumstances. One bad consequence is we are
emitting GOT for all accesses to all extern objects with default
visibility. The use of GOT is not needed in statically linked
executables, OS kernels etc. The GOT entry just wastes space, and the
GOT access just slow down the execution in those environments.
Before -mexplicit-relocs, we used "-Wa,-mla-global-with-pcrel" to tell
the assembler not to use GOT for extern access. But with
-mexplicit-relocs, we have to opt the logic in GCC.
The name "-mdirect-extern-access" is learnt from x86 port.
gcc/ChangeLog:
* config/loongarch/genopts/loongarch.opt.in: Add
-mdirect-extern-access option.
* config/loongarch/loongarch.opt: Regenerate.
* config/loongarch/loongarch.cc (loongarch_classify_symbol):
Don't use SYMBOL_GOT_DISP if TARGET_DIRECT_EXTERN_ACCESS.
(loongarch_option_override_internal): Complain if
-mdirect-extern-access is used with -fPIC or -fpic.
* doc/invoke.texi: Document -mdirect-extern-access for
LoongArch.
gcc/testsuite/ChangeLog:
* gcc.target/loongarch/direct-extern-1.c: New test.
* gcc.target/loongarch/direct-extern-2.c: New test.
---
gcc/config/loongarch/genopts/loongarch.opt.in | 4 ++++
gcc/config/loongarch/loongarch.cc | 5 ++++-
gcc/config/loongarch/loongarch.opt | 4 ++++
gcc/doc/invoke.texi | 15 +++++++++++++++
.../gcc.target/loongarch/direct-extern-1.c | 6 ++++++
.../gcc.target/loongarch/direct-extern-2.c | 6 ++++++
6 files changed, 39 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/gcc.target/loongarch/direct-extern-1.c
create mode 100644 gcc/testsuite/gcc.target/loongarch/direct-extern-2.c
diff --git a/gcc/config/loongarch/genopts/loongarch.opt.in
b/gcc/config/loongarch/genopts/loongarch.opt.in
index ebdd9538d48..e10618777b2 100644
--- a/gcc/config/loongarch/genopts/loongarch.opt.in
+++ b/gcc/config/loongarch/genopts/loongarch.opt.in
@@ -184,3 +184,7 @@ Enum(cmodel) String(@@STR_CMODEL_EXTREME@@)
Value(CMODEL_EXTREME)
mcmodel=
Target RejectNegative Joined Enum(cmodel) Var(la_opt_cmodel)
Init(CMODEL_NORMAL)
Specify the code model.
+
+mdirect-extern-access
+Target Var(TARGET_DIRECT_EXTERN_ACCESS) Init(0)
+Avoid using the GOT to access external symbols.
diff --git a/gcc/config/loongarch/loongarch.cc
b/gcc/config/loongarch/loongarch.cc
index 77e3a105390..2875fa5b0f3 100644
--- a/gcc/config/loongarch/loongarch.cc
+++ b/gcc/config/loongarch/loongarch.cc
@@ -1642,7 +1642,7 @@ loongarch_classify_symbol (const_rtx x)
if (SYMBOL_REF_TLS_MODEL (x))
return SYMBOL_TLS;
- if (!loongarch_symbol_binds_local_p (x))
+ if (!TARGET_DIRECT_EXTERN_ACCESS && !loongarch_symbol_binds_local_p (x))
return SYMBOL_GOT_DISP;
tree t = SYMBOL_REF_DECL (x);
@@ -6093,6 +6093,9 @@ loongarch_option_override_internal (struct gcc_options
*opts)
if (loongarch_branch_cost == 0)
loongarch_branch_cost = loongarch_cost->branch_cost;
+ if (TARGET_DIRECT_EXTERN_ACCESS && flag_shlib)
+ error ("%qs cannot be used for compiling a shared library",
+ "-mdirect-extern-access");
switch (la_target.cmodel)
{
diff --git a/gcc/config/loongarch/loongarch.opt
b/gcc/config/loongarch/loongarch.opt
index 6395234218b..96c811c850b 100644
--- a/gcc/config/loongarch/loongarch.opt
+++ b/gcc/config/loongarch/loongarch.opt
@@ -191,3 +191,7 @@ Enum(cmodel) String(extreme) Value(CMODEL_EXTREME)
mcmodel=
Target RejectNegative Joined Enum(cmodel) Var(la_opt_cmodel)
Init(CMODEL_NORMAL)
Specify the code model.
+
+mdirect-extern-access
+Target Var(TARGET_DIRECT_EXTERN_ACCESS) Init(0)
+Avoid using the GOT to access external symbols.
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index e5eb525a2c1..d4e86682827 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -1016,6 +1016,7 @@ Objective-C and Objective-C++ Dialects}.
-memcpy -mno-memcpy -mstrict-align -mno-strict-align @gol
-mmax-inline-memcpy-size=@var{n} @gol
-mexplicit-relocs -mno-explicit-relocs @gol
+-mdirect-extern-access -mno-direct-extern-access @gol
-mcmodel=@var{code-model}}
@emph{M32R/D Options}
@@ -25100,6 +25101,20 @@ GCC build-time by detecting corresponding assembler
support:
@code{-mno-explicit-relocs} otherwise. This option is mostly useful for
debugging, or interoperation with assemblers different from the build-time
one.
+
+@item -mdirect-extern-access
+@itemx -mno-direct-extern-access
+@opindex mdirect-extern-access
+Do not use or use GOT to access external symbols. The default is
+@option{-mno-direct-extern-access}: GOT is used for external symbols with
+default visibility, but not used for other external symbols.
+
+With @option{-mdirect-extern-access}, GOT is not used and all external
+symbols are PC-relatively addressed. It is @strong{only} suitable for
+environments where no dynamic link is performed, like firmwares, OS
+kernels, executables linked with @option{-static} or @option{-static-pie}.
+@option{-mdirect-extern-access} is not compatible with @option{-fPIC} or
+@option{-fpic}.
@end table
@node M32C Options
diff --git a/gcc/testsuite/gcc.target/loongarch/direct-extern-1.c
b/gcc/testsuite/gcc.target/loongarch/direct-extern-1.c
new file mode 100644
index 00000000000..85c6c1e8a88
--- /dev/null
+++ b/gcc/testsuite/gcc.target/loongarch/direct-extern-1.c
@@ -0,0 +1,6 @@
+/* { dg-do compile } */
+/* { dg-options "-mexplicit-relocs -mdirect-extern-access" } */
+/* { dg-final { scan-assembler-not "got" } } */
+
+extern int x;
+int f() { return x; }
diff --git a/gcc/testsuite/gcc.target/loongarch/direct-extern-2.c
b/gcc/testsuite/gcc.target/loongarch/direct-extern-2.c
new file mode 100644
index 00000000000..58d8bd68a06
--- /dev/null
+++ b/gcc/testsuite/gcc.target/loongarch/direct-extern-2.c
@@ -0,0 +1,6 @@
+/* { dg-do compile } */
+/* { dg-options "-mno-explicit-relocs -mdirect-extern-access" } */
+/* { dg-final { scan-assembler-not "la.global" } } */
+
+extern int x;
+int f() { return x; }
--
2.37.3
