[glibc] riscv: Resolve symbols directly for symbols with STO_RISCV_VARIANT_CC.

[glibc] riscv: Resolve symbols directly for symbols with STO_RISCV_VARIANT_CC.

[Palmer Dabbelt]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=117e8b341c5c0ace8d65feeef136fececb3fdc9c

commit 117e8b341c5c0ace8d65feeef136fececb3fdc9c
Author: Hsiangkai Wang <kai.wang@sifive.com>
Date:   Wed Mar 15 00:25:12 2023 +0800

    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>
    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>

Diff:
---
 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(+)

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
+
 /* 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)