Fwd: [COMMITTED 1/2] riscv: Resolve symbols directly for symbols with STO_RISCV_VARIANT_CC.

[Manjul Mohan]

>
>
> From: Hsiangkai Wang <kai.wang@sifive.com>
>
> 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>
> Reviewed-by: Palmer Dabbelt <palmer@rivosinc.com>
> Acked-by: Palmer Dabbelt <palmer@rivosinc.com>
> Link: 
> https://inbox.sourceware.org/libc-alpha/20230314162512.35802-1-kito.cheng@sifive.com
> Signed-off-by: Palmer Dabbelt <palmer@rivosinc.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 94ca23c1bb..4f65b5a32d 100644
> --- a/elf/elf.h
> +++ b/elf/elf.h
> @@ -3933,6 +3933,13 @@ 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


This is causing  testcase failures on ppc64le platform.

/../elf/elf.h:4013: error: macro STO_RISCV_VARIANT_CC redefined
//../elf/elf.h:3941: note: location of previous definition
../elf/elf.h:4023: error: macro DT_RISCV_VARIANT_CC redefined
../elf/elf.h:3937: note: location of previous definition

Testcase failures:
elf/tst-glibcelf
elf/tst-relro-ldso
elf/tst-relro-libc

> +
> /* 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 c6ed73cb97..714c07813f 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..281c5aadeb
> --- /dev/null
> +++ b/sysdeps/riscv/dl-dtprocnum.h
> @@ -0,0 +1,21 @@
> +/* Configuration of lookup functions. RISC-V version.
> + Copyright (C) 2023 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 c0c9bd93ad..0e6c0bb155 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)
> -- 
> 2.40.0
>