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- From 66e355177a3c5f637852e47290878e06a7f95c32 Mon Sep 17 00:00:00 2001
- From: Hsiangkai Wang <kai.wang@sifive.com>
- Date: Tue, 18 Jan 2022 12:31:59 +0800
- Subject: [PATCH 05/19] riscv: Resolve symbols directly for symbols with
- STO_RISCV_VARIANT_CC.
- In some cases, we do not want to go through the resolver for function
- calls. For example, functions with vector arguments will use vector
- registers to pass arguments. In the resolver, we do not save/restore the
- vector argument registers for lazy binding efficiency. To avoid ruining
- the vector arguments, functions with vector arguments will not go
- through the resolver.
- To achieve the goal, we will annotate the function symbols with
- STO_RISCV_VARIANT_CC flag and add DT_RISCV_VARIANT_CC tag in the dynamic
- section. In the first pass on PLT relocations, we do not set up to call
- _dl_runtime_resolve. Instead, we resolve the functions directly.
- Signed-off-by: Hsiangkai Wang <kai.wang@sifive.com>
- Signed-off-by: Vincent Chen <vincent.chen@sifive.com>
- ---
- elf/elf.h | 7 +++++++
- manual/platform.texi | 6 ++++++
- sysdeps/riscv/dl-dtprocnum.h | 21 +++++++++++++++++++++
- sysdeps/riscv/dl-machine.h | 26 ++++++++++++++++++++++++++
- 4 files changed, 60 insertions(+)
- create mode 100644 sysdeps/riscv/dl-dtprocnum.h
- diff --git a/elf/elf.h b/elf/elf.h
- index 7d1571043d..27009bdbc0 100644
- --- a/elf/elf.h
- +++ b/elf/elf.h
- @@ -3925,6 +3925,13 @@ enum
-
- #define R_TILEGX_NUM 130
-
- +/* RISC-V specific values for the Dyn d_tag field. */
- +#define DT_RISCV_VARIANT_CC (DT_LOPROC + 1)
- +#define DT_RISCV_NUM 2
- +
- +/* RISC-V specific values for the st_other field. */
- +#define STO_RISCV_VARIANT_CC 0x80
- +
- /* RISC-V ELF Flags */
- #define EF_RISCV_RVC 0x0001
- #define EF_RISCV_FLOAT_ABI 0x0006
- diff --git a/manual/platform.texi b/manual/platform.texi
- index d5fdc5bd05..a1a740f381 100644
- --- a/manual/platform.texi
- +++ b/manual/platform.texi
- @@ -121,6 +121,12 @@ when it is not allowed, the priority is set to medium.
- @node RISC-V
- @appendixsec RISC-V-specific Facilities
-
- +Functions that are lazily bound must be compatible with the standard calling
- +convention. When a function is annotated with STO_RISCV_VARIANT_CC, it means
- +this function is not compatible with the standard calling convention. The
- +dynamic linker will directly resolve it instead of using the lazy binding
- +mechanism.
- +
- Cache management facilities specific to RISC-V systems that implement the Linux
- ABI are declared in @file{sys/cachectl.h}.
-
- diff --git a/sysdeps/riscv/dl-dtprocnum.h b/sysdeps/riscv/dl-dtprocnum.h
- new file mode 100644
- index 0000000000..f189fd700a
- --- /dev/null
- +++ b/sysdeps/riscv/dl-dtprocnum.h
- @@ -0,0 +1,21 @@
- +/* Configuration of lookup functions. RISC-V version.
- + Copyright (C) 2019-2021 Free Software Foundation, Inc.
- + This file is part of the GNU C Library.
- +
- + The GNU C Library is free software; you can redistribute it and/or
- + modify it under the terms of the GNU Lesser General Public
- + License as published by the Free Software Foundation; either
- + version 2.1 of the License, or (at your option) any later version.
- +
- + The GNU C Library is distributed in the hope that it will be useful,
- + but WITHOUT ANY WARRANTY; without even the implied warranty of
- + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
- + Lesser General Public License for more details.
- +
- + You should have received a copy of the GNU Lesser General Public
- + License along with the GNU C Library. If not, see
- + <https://www.gnu.org/licenses/>. */
- +
- +/* Number of extra dynamic section entries for this architecture. By
- + default there are none. */
- +#define DT_THISPROCNUM DT_RISCV_NUM
- diff --git a/sysdeps/riscv/dl-machine.h b/sysdeps/riscv/dl-machine.h
- index dfedc9801d..11523ae627 100644
- --- a/sysdeps/riscv/dl-machine.h
- +++ b/sysdeps/riscv/dl-machine.h
- @@ -53,6 +53,9 @@
- || (__WORDSIZE == 64 && (type) == R_RISCV_TLS_TPREL64))) \
- | (ELF_RTYPE_CLASS_COPY * ((type) == R_RISCV_COPY)))
-
- +//* Translate a processor specific dynamic tag to the index in l_info array. */
- +#define DT_RISCV(x) (DT_RISCV_##x - DT_LOPROC + DT_NUM)
- +
- /* Return nonzero iff ELF header is compatible with the running host. */
- static inline int __attribute_used__
- elf_machine_matches_host (const ElfW(Ehdr) *ehdr)
- @@ -281,6 +284,29 @@ elf_machine_lazy_rel (struct link_map *map, struct r_scope_elem *scope[],
- /* Check for unexpected PLT reloc type. */
- if (__glibc_likely (r_type == R_RISCV_JUMP_SLOT))
- {
- + if (__glibc_unlikely (map->l_info[DT_RISCV (VARIANT_CC)] != NULL))
- + {
- + /* Check the symbol table for variant CC symbols. */
- + const Elf_Symndx symndx = ELFW(R_SYM) (reloc->r_info);
- + const ElfW(Sym) *symtab =
- + (const void *)D_PTR (map, l_info[DT_SYMTAB]);
- + const ElfW(Sym) *sym = &symtab[symndx];
- + if (__glibc_unlikely (sym->st_other & STO_RISCV_VARIANT_CC))
- + {
- + /* Avoid lazy resolution of variant CC symbols. */
- + const struct r_found_version *version = NULL;
- + if (map->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
- + {
- + const ElfW(Half) *vernum =
- + (const void *)D_PTR (map, l_info[VERSYMIDX (DT_VERSYM)]);
- + version = &map->l_versions[vernum[symndx] & 0x7fff];
- + }
- + elf_machine_rela (map, scope, reloc, sym, version, reloc_addr,
- + skip_ifunc);
- + return;
- + }
- + }
- +
- if (__glibc_unlikely (map->l_mach.plt == 0))
- {
- if (l_addr)
- --
- 2.25.1
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