When using -mcmodel=medium, large data objects larger than the -mlarge-data-threshold threshold are placed into large data sections (.lrodata, .ldata, .lbss and some variants). GNU ld and ld.lld 17 place .l* sections into separate output sections. If small and medium code model object files are mixed, the .l* sections won't exert relocation overflow pressure on sections in object files built with -mcmodel=small.
However, when using -mcmodel=large, -mlarge-data-threshold doesn't apply. This means that the .rodata/.data/.bss sections may exert relocation overflow pressure on sections in -mcmodel=small object files. This patch allows -mcmodel=large to generate .l* sections and drops an unneeded documentation restriction that the value must be the same. Link: https://groups.google.com/g/x86-64-abi/c/jnQdJeabxiU ("Large data sections for the large code model") Signed-off-by: Fangrui Song <mask...@google.com> --- Changes from v1 (https://gcc.gnu.org/pipermail/gcc-patches/2023-April/616947.html): * Clarify commit message. Add link to https://groups.google.com/g/x86-64-abi/c/jnQdJeabxiU Changes from v2 * Drop an uneeded limitation in the documentation. Changes from v3 * Change scan-assembler directives to use \. to match literal . --- gcc/config/i386/i386.cc | 15 +++++++++------ gcc/config/i386/i386.opt | 2 +- gcc/doc/invoke.texi | 6 +++--- gcc/testsuite/gcc.target/i386/large-data.c | 13 +++++++++++++ 4 files changed, 26 insertions(+), 10 deletions(-) create mode 100644 gcc/testsuite/gcc.target/i386/large-data.c diff --git a/gcc/config/i386/i386.cc b/gcc/config/i386/i386.cc index eabc70011ea..37e810cc741 100644 --- a/gcc/config/i386/i386.cc +++ b/gcc/config/i386/i386.cc @@ -647,7 +647,8 @@ ix86_can_inline_p (tree caller, tree callee) static bool ix86_in_large_data_p (tree exp) { - if (ix86_cmodel != CM_MEDIUM && ix86_cmodel != CM_MEDIUM_PIC) + if (ix86_cmodel != CM_MEDIUM && ix86_cmodel != CM_MEDIUM_PIC && + ix86_cmodel != CM_LARGE && ix86_cmodel != CM_LARGE_PIC) return false; if (exp == NULL_TREE) @@ -858,8 +859,9 @@ x86_elf_aligned_decl_common (FILE *file, tree decl, const char *name, unsigned HOST_WIDE_INT size, unsigned align) { - if ((ix86_cmodel == CM_MEDIUM || ix86_cmodel == CM_MEDIUM_PIC) - && size > (unsigned int)ix86_section_threshold) + if ((ix86_cmodel == CM_MEDIUM || ix86_cmodel == CM_MEDIUM_PIC || + ix86_cmodel == CM_LARGE || ix86_cmodel == CM_LARGE_PIC) && + size > (unsigned int)ix86_section_threshold) { switch_to_section (get_named_section (decl, ".lbss", 0)); fputs (LARGECOMM_SECTION_ASM_OP, file); @@ -879,9 +881,10 @@ void x86_output_aligned_bss (FILE *file, tree decl, const char *name, unsigned HOST_WIDE_INT size, unsigned align) { - if ((ix86_cmodel == CM_MEDIUM || ix86_cmodel == CM_MEDIUM_PIC) - && size > (unsigned int)ix86_section_threshold) - switch_to_section (get_named_section (decl, ".lbss", 0)); + if ((ix86_cmodel == CM_MEDIUM || ix86_cmodel == CM_MEDIUM_PIC || + ix86_cmodel == CM_LARGE || ix86_cmodel == CM_LARGE_PIC) && + size > (unsigned int)ix86_section_threshold) + switch_to_section(get_named_section(decl, ".lbss", 0)); else switch_to_section (bss_section); ASM_OUTPUT_ALIGN (file, floor_log2 (align / BITS_PER_UNIT)); diff --git a/gcc/config/i386/i386.opt b/gcc/config/i386/i386.opt index 1cc8563477a..52fad492353 100644 --- a/gcc/config/i386/i386.opt +++ b/gcc/config/i386/i386.opt @@ -282,7 +282,7 @@ Branches are this expensive (arbitrary units). mlarge-data-threshold= Target RejectNegative Joined UInteger Var(ix86_section_threshold) Init(DEFAULT_LARGE_SECTION_THRESHOLD) --mlarge-data-threshold=<number> Data greater than given threshold will go into .ldata section in x86-64 medium model. +-mlarge-data-threshold=<number> Data greater than given threshold will go into a large data section in x86-64 medium and large code models. mcmodel= Target RejectNegative Joined Enum(cmodel) Var(ix86_cmodel) Init(CM_32) diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi index 104766f446d..bf6fe3e1a20 100644 --- a/gcc/doc/invoke.texi +++ b/gcc/doc/invoke.texi @@ -33207,9 +33207,9 @@ the cache line size. @samp{compat} is the default. @opindex mlarge-data-threshold @item -mlarge-data-threshold=@var{threshold} -When @option{-mcmodel=medium} is specified, data objects larger than -@var{threshold} are placed in the large data section. This value must be the -same across all objects linked into the binary, and defaults to 65535. +When @option{-mcmodel=medium} or @option{-mcmodel=large} is specified, data +objects larger than @var{threshold} are placed in large data sections. The +default is 65535. @opindex mrtd @item -mrtd diff --git a/gcc/testsuite/gcc.target/i386/large-data.c b/gcc/testsuite/gcc.target/i386/large-data.c new file mode 100644 index 00000000000..bdd4acd30b8 --- /dev/null +++ b/gcc/testsuite/gcc.target/i386/large-data.c @@ -0,0 +1,13 @@ +/* { dg-do compile } */ +/* { dg-require-effective-target lp64 } */ +/* { dg-options "-O2 -mcmodel=large -mlarge-data-threshold=4" } */ +/* { dg-final { scan-assembler {\.lbss} } } */ +/* { dg-final { scan-assembler {\.bss} } } */ +/* { dg-final { scan-assembler {\.ldata} } } */ +/* { dg-final { scan-assembler {\.data} } } */ +/* { dg-final { scan-assembler {\.lrodata} } } */ +/* { dg-final { scan-assembler {\.rodata} } } */ + +const char rodata_a[] = "abc", rodata_b[] = "abcd"; +char data_a[4] = {1}, data_b[5] = {1}; +char bss_a[4], bss_b[5]; -- 2.41.0.585.gd2178a4bd4-goog
