As it has been discussed on timens RFC, adding a new conditional branch
`if (inside_time_ns)` on VDSO for all processes is undesirable.
Addressing those problems, there are two versions of VDSO's .so:
for host tasks (without any penalty) and for processes inside time
namespace with clk_to_ns() that subtracts offsets from host's time.
The timens code in vdso looks like this:
if (timens_static_branch()) {
clk_to_ns(clk, ts);
}
Static branch mechanism adds a __jump_table section into vdso.
Vdso's linker script drops all unwanted sections in compile time.
Preserve __jump_table section and add it into (struct vdso_image),
as it's needed for enabling (patching) static branches that are
present on vdso.
Co-developed-by: Andrei Vagin <ava...@gmail.com>
Signed-off-by: Andrei Vagin <ava...@gmail.com>
Signed-off-by: Dmitry Safonov <d...@arista.com>
---
arch/x86/entry/vdso/vdso-layout.lds.S | 1 +
arch/x86/entry/vdso/vdso2c.h | 9 ++++++++-
arch/x86/include/asm/vdso.h | 1 +
3 files changed, 10 insertions(+), 1 deletion(-)
diff --git a/arch/x86/entry/vdso/vdso-layout.lds.S
b/arch/x86/entry/vdso/vdso-layout.lds.S
index ba216527e59f..69dbe4821aa5 100644
--- a/arch/x86/entry/vdso/vdso-layout.lds.S
+++ b/arch/x86/entry/vdso/vdso-layout.lds.S
@@ -45,6 +45,7 @@ SECTIONS
.gnu.version : { *(.gnu.version) }
.gnu.version_d : { *(.gnu.version_d) }
.gnu.version_r : { *(.gnu.version_r) }
+ __jump_table : { *(__jump_table) } :text
.dynamic : { *(.dynamic) } :text :dynamic
diff --git a/arch/x86/entry/vdso/vdso2c.h b/arch/x86/entry/vdso/vdso2c.h
index 885b988aea19..318b278ca396 100644
--- a/arch/x86/entry/vdso/vdso2c.h
+++ b/arch/x86/entry/vdso/vdso2c.h
@@ -14,7 +14,7 @@ static void BITSFUNC(go)(void *raw_addr, size_t raw_len,
unsigned long mapping_size;
ELF(Ehdr) *hdr = (ELF(Ehdr) *)raw_addr;
unsigned int i, syms_nr;
- unsigned long j;
+ unsigned long j, jump_table_addr = -1UL, jump_table_size = -1UL;
ELF(Shdr) *symtab_hdr = NULL, *strtab_hdr, *secstrings_hdr,
*alt_sec = NULL;
ELF(Dyn) *dyn = 0, *dyn_end = 0;
@@ -78,6 +78,10 @@ static void BITSFUNC(go)(void *raw_addr, size_t raw_len,
if (!strcmp(secstrings + GET_LE(&sh->sh_name),
".altinstructions"))
alt_sec = sh;
+ if (!strcmp(secstrings + GET_LE(&sh->sh_name), "__jump_table"))
{
+ jump_table_addr = GET_LE(&sh->sh_offset);
+ jump_table_size = GET_LE(&sh->sh_size);
+ }
}
if (!symtab_hdr)
@@ -166,6 +170,9 @@ static void BITSFUNC(go)(void *raw_addr, size_t raw_len,
fprintf(outfile, "\t.alt_len = %lu,\n",
(unsigned long)GET_LE(&alt_sec->sh_size));
}
+ fprintf(outfile, "\t.jump_table = %luUL,\n", jump_table_addr);
+ fprintf(outfile, "\t.jump_table_len = %luUL,\n", jump_table_size);
+
for (i = 0; i < NSYMS; i++) {
if (required_syms[i].export && syms[i])
fprintf(outfile, "\t.sym_%s = %" PRIi64 ",\n",
diff --git a/arch/x86/include/asm/vdso.h b/arch/x86/include/asm/vdso.h
index ccf89dedd04f..5e83bd3cda22 100644
--- a/arch/x86/include/asm/vdso.h
+++ b/arch/x86/include/asm/vdso.h
@@ -16,6 +16,7 @@ struct vdso_image {
unsigned long size; /* Always a multiple of PAGE_SIZE */
unsigned long alt, alt_len;
+ unsigned long jump_table, jump_table_len;
long sym_vvar_start; /* Negative offset to the vvar area */
--
2.22.0
