[PATCH 2/2] riscv: Initialize $gp before resolving the IRELATIVE relocation
Vincent Chen
vincent.chen@sifive.com
Tue Dec 1 10:23:00 GMT 2020
RISC-V $gp register may be used to access the global variable in
the PDE program. Currently, the initialization of $gp register
is addressed in the _start function. However, the IFUNC resolver is
executed before the _start function. In this condition, if a IFUNC
resolver function uses the uninitialized $gp to access global variable,
an unexpected error will occur. This patch makes ld.so initialize
the $gp with the DT_RISCV_GP dynamic entry before resolving the
IRELATIVE symbol.
---
elf/elf.h | 4 ++++
sysdeps/riscv/dl-dtprocnum.h | 22 ++++++++++++++++++++++
sysdeps/riscv/dl-machine.h | 9 +++++++++
3 files changed, 35 insertions(+)
create mode 100644 sysdeps/riscv/dl-dtprocnum.h
diff --git a/elf/elf.h b/elf/elf.h
index 6439c1a4d5..7566da2dca 100644
--- a/elf/elf.h
+++ b/elf/elf.h
@@ -3955,6 +3955,10 @@ enum
#define R_RISCV_NUM 59
+/* RISCV specific values for the Dyn d_tag field. */
+#define DT_RISCV_GP (DT_LOPROC + 0)
+#define DT_RISCV_NUM 1
+
/* BPF specific declarations. */
#define R_BPF_NONE 0 /* No reloc */
diff --git a/sysdeps/riscv/dl-dtprocnum.h b/sysdeps/riscv/dl-dtprocnum.h
new file mode 100644
index 0000000000..5b5f99571a
--- /dev/null
+++ b/sysdeps/riscv/dl-dtprocnum.h
@@ -0,0 +1,22 @@
+/* Configuration of lookup functions. RISC-V version.
+ Copyright (C) 2020 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 0ae45dd0c3..4b1b8e1444 100644
--- a/sysdeps/riscv/dl-machine.h
+++ b/sysdeps/riscv/dl-machine.h
@@ -54,6 +54,9 @@
#define ELF_MACHINE_NO_REL 1
#define ELF_MACHINE_NO_RELA 0
+/* Translate a RISC-V 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)
@@ -341,6 +344,12 @@ elf_machine_runtime_setup (struct link_map *l, int lazy, int profile)
}
#endif
+ if (l->l_info[DT_RISCV(GP)])
+ asm (
+ "mv gp, %0\n"
+ :
+ :"r"(D_PTR (l, l_info[DT_RISCV(GP)]))
+ );
return lazy;
}
--
2.29.2
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