110 lines
4.6 KiB
Diff
110 lines
4.6 KiB
Diff
commit e7c570f37384d824cb9725f237920e9691e57269
|
|
gpg: Signature made Tue 06 Mar 2018 04:52:46 PM PST
|
|
gpg: using RSA key 00CE76D1834960DFCE886DF8EF4CA1502CCBAB41
|
|
gpg: issuer "palmer@dabbelt.com"
|
|
gpg: Good signature from "Palmer Dabbelt <palmer@dabbelt.com>" [ultimate]
|
|
gpg: aka "Palmer Dabbelt <palmer@sifive.com>" [ultimate]
|
|
Author: Palmer Dabbelt <palmer@sifive.com>
|
|
Date: Thu Mar 1 12:01:06 2018 -0800
|
|
|
|
RISC-V: Add and document the "-mno-relax" option
|
|
|
|
RISC-V relies on aggressive linker relaxation to get good code size. As
|
|
a result no text symbol addresses can be known until link time, which
|
|
means that alignment must be handled during the link. This alignment
|
|
pass is essentially just another linker relaxation, so this has the
|
|
unfortunate side effect that linker relaxation is required for
|
|
correctness on many RISC-V targets.
|
|
|
|
The RISC-V assembler has supported an ".option norelax" for a long time
|
|
because there are situations in which linker relaxation is a bad idea --
|
|
the canonical example is when trying to materialize the initial value of
|
|
the global pointer into a register, which would otherwise be relaxed to
|
|
a NOP. We've been relying on users who want to disable relaxation for
|
|
an entire link to pass "-Wl,--no-relax", but that still relies on the
|
|
linker relaxing R_RISCV_ALIGN to handle alignment despite it not being
|
|
strictly necessary.
|
|
|
|
This patch adds a GCC option, "-mno-relax", that disable linker
|
|
relaxation by adding ".option norelax" to the top of every generated
|
|
assembly file. The assembler is smart enough to handle alignment at
|
|
assemble time for files that have never emitted a relaxable relocation,
|
|
so this is sufficient to really disable all relaxations in the linker,
|
|
which results in significantly faster link times for large objects.
|
|
|
|
This also has the side effect of allowing toolchains that don't support
|
|
linker relaxation (LLVM and the Linux module loader) to function
|
|
correctly. Toolchains that don't support linker relaxation should
|
|
default to "-mno-relax" and error when presented with any R_RISCV_ALIGN
|
|
relocation as those need to be handled for correctness.
|
|
|
|
gcc/ChangeLog
|
|
|
|
2018-03-01 Palmer Dabbelt <palmer@sifive.com>
|
|
|
|
* config/riscv/riscv.opt (mrelax): New option.
|
|
* config/riscv/riscv.c (riscv_file_start): Emit ".option
|
|
"norelax" when riscv_mrelax is disabled.
|
|
* doc/invoke.texi (RISC-V): Document "-mrelax" and "-mno-relax".
|
|
|
|
diff --git a/gcc/config/riscv/riscv.c b/gcc/config/riscv/riscv.c
|
|
index c38f6c394d54..3e81874de232 100644
|
|
--- a/gcc/config/riscv/riscv.c
|
|
+++ b/gcc/config/riscv/riscv.c
|
|
@@ -3979,6 +3979,11 @@ riscv_file_start (void)
|
|
|
|
/* Instruct GAS to generate position-[in]dependent code. */
|
|
fprintf (asm_out_file, "\t.option %spic\n", (flag_pic ? "" : "no"));
|
|
+
|
|
+ /* If the user specifies "-mno-relax" on the command line then disable linker
|
|
+ relaxation in the assembler. */
|
|
+ if (! riscv_mrelax)
|
|
+ fprintf (asm_out_file, "\t.option norelax\n");
|
|
}
|
|
|
|
/* Implement TARGET_ASM_OUTPUT_MI_THUNK. Generate rtl rather than asm text
|
|
diff --git a/gcc/config/riscv/riscv.opt b/gcc/config/riscv/riscv.opt
|
|
index 581a26bb5c1e..b37ac75d9bb4 100644
|
|
--- a/gcc/config/riscv/riscv.opt
|
|
+++ b/gcc/config/riscv/riscv.opt
|
|
@@ -106,6 +106,11 @@ mexplicit-relocs
|
|
Target Report Mask(EXPLICIT_RELOCS)
|
|
Use %reloc() operators, rather than assembly macros, to load addresses.
|
|
|
|
+mrelax
|
|
+Target Bool Var(riscv_mrelax) Init(1)
|
|
+Take advantage of linker relaxations to reduce the number of instructions
|
|
+required to materialize symbol addresses.
|
|
+
|
|
Mask(64BIT)
|
|
|
|
Mask(MUL)
|
|
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
|
|
index 8d366c626bae..deb48af2ecad 100644
|
|
--- a/gcc/doc/invoke.texi
|
|
+++ b/gcc/doc/invoke.texi
|
|
@@ -1042,7 +1042,8 @@ See RS/6000 and PowerPC Options.
|
|
-msave-restore -mno-save-restore @gol
|
|
-mstrict-align -mno-strict-align @gol
|
|
-mcmodel=medlow -mcmodel=medany @gol
|
|
--mexplicit-relocs -mno-explicit-relocs @gol}
|
|
+-mexplicit-relocs -mno-explicit-relocs @gol
|
|
+-mrelax -mno-relax @gol}
|
|
|
|
@emph{RL78 Options}
|
|
@gccoptlist{-msim -mmul=none -mmul=g13 -mmul=g14 -mallregs @gol
|
|
@@ -23102,6 +23103,12 @@ Use or do not use assembler relocation operators when dealing with symbolic
|
|
addresses. The alternative is to use assembler macros instead, which may
|
|
limit optimization.
|
|
|
|
+@item -mrelax
|
|
+@itemx -mno-relax
|
|
+Take advantage of linker relaxations to reduce the number of instructions
|
|
+required to materialize symbol addresses. The default is to take advantage of
|
|
+linker relaxations.
|
|
+
|
|
@end table
|
|
|
|
@node RL78 Options
|
|
|