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bbcc5672b0
Declaring __current_thread_info as a global register variable has the effect of preventing GCC from saving & restoring its value in cases where the ABI would typically do so. To quote GCC documentation: > If the register is a call-saved register, call ABI is affected: the > register will not be restored in function epilogue sequences after the > variable has been assigned. Therefore, functions cannot safely return > to callers that assume standard ABI. When our position independent VDSO is built for the n32 or n64 ABIs all functions it exposes should be preserving the value of $gp/$28 for their caller, but in the presence of the __current_thread_info global register variable GCC stops doing so & simply clobbers $gp/$28 when calculating the address of the GOT. In cases where the VDSO returns success this problem will typically be masked by the caller in libc returning & restoring $gp/$28 itself, but that is by no means guaranteed. In cases where the VDSO returns an error libc will typically contain a fallback path which will now fail (typically with a bad memory access) if it attempts anything which relies upon the value of $gp/$28 - eg. accessing anything via the GOT. One fix for this would be to move the declaration of __current_thread_info inside the current_thread_info() function, demoting it from global register variable to local register variable & avoiding inadvertently creating a non-standard calling ABI for the VDSO. Unfortunately this causes issues for clang, which doesn't support local register variables as pointed out by commit |
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arch | ||
block | ||
certs | ||
crypto | ||
Documentation | ||
drivers | ||
fs | ||
include | ||
init | ||
ipc | ||
kernel | ||
lib | ||
LICENSES | ||
mm | ||
net | ||
samples | ||
scripts | ||
security | ||
sound | ||
tools | ||
usr | ||
virt | ||
.clang-format | ||
.cocciconfig | ||
.get_maintainer.ignore | ||
.gitattributes | ||
.gitignore | ||
.mailmap | ||
COPYING | ||
CREDITS | ||
Kbuild | ||
Kconfig | ||
MAINTAINERS | ||
Makefile | ||
README |
Linux kernel ============ There are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. Please read Documentation/admin-guide/README.rst first. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. The formatted documentation can also be read online at: https://www.kernel.org/doc/html/latest/ There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.