CONFIG_COMPAT_VDSO: Disable the 32-bit vDSO (needed for glibc 2.3.3)

General informations

The Linux kernel configuration item CONFIG_COMPAT_VDSO has multiple definitions:

Disable the 32-bit vDSO (needed for glibc 2.3.3) found in arch/x86/Kconfig

The configuration item CONFIG_COMPAT_VDSO:

• prompt: Disable the 32-bit vDSO (needed for glibc 2.3.3)
• type: bool
• depends on: CONFIG_COMPAT_32
• defined in arch/x86/Kconfig
• found in Linux kernels: 3.15–3.19, 4.0–4.20, 5.0–5.19, 6.0–6.8, 6.9-rc+HEAD

Help text

Certain buggy versions of glibc will crash if they are presented with a 32-bit vDSO that is not mapped at the address indicated in its segment table.

The bug was introduced by f866314b89d56845f55e6f365e18b31ec978ec3a and fixed by 3b3ddb4f7db98ec9e912ccdf54d35df4aa30e04a and 49ad572a70b8aeb91e57483a11dd1b77e31c4468. Glibc 2.3.3 is the only released version with the bug, but OpenSUSE 9 contains a buggy "glibc 2.3.2".

The symptom of the bug is that everything crashes on startup, saying: dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!

Saying Y here changes the default value of the vdso32 boot option from 1 to 0, which turns off the 32-bit vDSO entirely. This works around the glibc bug but hurts performance.

If unsure, say N: if you are compiling your own kernel, you are unlikely to be using a buggy version of glibc.

Enable vDSO for 32-bit applications found in arch/arm64/Kconfig

The configuration item CONFIG_COMPAT_VDSO:

• prompt: Enable vDSO for 32-bit applications
• type: bool
• depends on: (! CONFIG_CPU_BIG_ENDIAN ) && (( CONFIG_CC_IS_CLANG && CONFIG_LD_IS_LLD ) || "$( CONFIG_CROSS_COMPILE_COMPAT )" != "")
• defined in arch/arm64/Kconfig
• found in Linux kernels: 5.4–5.19, 6.0–6.8, 6.9-rc+HEAD

Help text

Place in the process address space of 32-bit applications an ELF shared object providing fast implementations of gettimeofday and clock_gettime.

You must have a 32-bit build of glibc 2.22 or later for programs to seamlessly take advantage of this.

found in arch/s390/Kconfig

The configuration item CONFIG_COMPAT_VDSO:

• prompt:
• type: bool
• depends on: (none)
• defined in arch/s390/Kconfig
• found in Linux kernels: 5.2–5.4

Help text

(none)

Compat VDSO support found in arch/x86/Kconfig

The configuration item CONFIG_COMPAT_VDSO:

• prompt: Compat VDSO support
• type: bool
• depends on: CONFIG_X86_32 || CONFIG_IA32_EMULATION
• defined in arch/x86/Kconfig
• found in Linux kernels: 2.6.24–2.6.39, 3.0–3.14

Help text

Map the 32-bit VDSO to the predictable old-style address too.

Say N here if you are running a sufficiently recent glibc version (2.3.3 or later), to remove the high-mapped VDSO mapping and to exclusively use the randomized VDSO.

If unsure, say Y.

Compat VDSO support found in arch/i386/Kconfig

The configuration item CONFIG_COMPAT_VDSO:

• prompt: Compat VDSO support
• type: bool
• depends on: (none)
• defined in arch/i386/Kconfig
• found in Linux kernels: 2.6.18–2.6.23

Help text

Map the VDSO to the predictable old-style address too. Say N here if you are running a sufficiently recent glibc version (2.3.3 or later), to remove the high-mapped VDSO mapping and to exclusively use the randomized VDSO.

If unsure, say Y.

Hardware

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The data is retrived from:

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• Linux Kernel Driver DataBase (LKDDb)

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