I've been experimenting with enabling CONFIG_GCC_PLUGINS in the kernel since I've heard some people express interest in stackleak (I'm interested as well). a gcc plugin gets built as an .so file for use during compilation. This means we need to package this .so file as part of kernel-devel for building external modules. This is easy to do but it also now introduces a tighter restriction on the toolchain used for building modules since gcc will refuse to load a plugin and fail to build the module if the versions don't match. Arguably, there's always been a requirement to use the same toolchain version but there may have been some flexibility for forcing it.
Can anyone see major problems with requiring the same toolchain version for building external modules as the kernel?
Thanks, Laura
* Laura Abbott:
I've been experimenting with enabling CONFIG_GCC_PLUGINS in the kernel since I've heard some people express interest in stackleak (I'm interested as well). a gcc plugin gets built as an .so file for use during compilation. This means we need to package this .so file as part of kernel-devel for building external modules. This is easy to do but it also now introduces a tighter restriction on the toolchain used for building modules since gcc will refuse to load a plugin and fail to build the module if the versions don't match. Arguably, there's always been a requirement to use the same toolchain version but there may have been some flexibility for forcing it.
Can anyone see major problems with requiring the same toolchain version for building external modules as the kernel?
If those kernel modules happen to build userspace components as well (and use the right build flags), then they have such a toolchain dependency already, indirectly through the annobin plugin.
The main caveat I see is that it is tricky to handle the version constraints correctly (both in the plugin and at the RPM level). For a long time, the annobin constraints were too tight.
Cc:ing Nick in case he wants to add any comments.
Thanks, Florian
On 2/15/19 3:47 AM, Florian Weimer wrote:
- Laura Abbott:
I've been experimenting with enabling CONFIG_GCC_PLUGINS in the kernel since I've heard some people express interest in stackleak (I'm interested as well). a gcc plugin gets built as an .so file for use during compilation. This means we need to package this .so file as part of kernel-devel for building external modules. This is easy to do but it also now introduces a tighter restriction on the toolchain used for building modules since gcc will refuse to load a plugin and fail to build the module if the versions don't match. Arguably, there's always been a requirement to use the same toolchain version but there may have been some flexibility for forcing it.
Can anyone see major problems with requiring the same toolchain version for building external modules as the kernel?
If those kernel modules happen to build userspace components as well (and use the right build flags), then they have such a toolchain dependency already, indirectly through the annobin plugin.
The main caveat I see is that it is tricky to handle the version constraints correctly (both in the plugin and at the RPM level). For a long time, the annobin constraints were too tight.
Most modules are probably not going to be compiling userspace components so I'm not too concerned there.
Thanks for the pointer to annobin though, I hadn't thought about how to actually specify the requirement in the rpm file. I'm not sure if this example convinces me I should do gcc plugins or it's not worth the hassle.
Laura
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Florian Weimer -
Laura Abbott