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Implement --enable-debuginfo to permit us to force building with debuginfo #392
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Currently, bogus options to --enable-debug become --disable-debug. That means that passing --enable-debug=true is analogous to --disable-debug, but the result is counterintuitive. We switch to AS_CASE to allow us to fail when given a bogus option. Also, we modify the text printed to clarify that --enable-debug enables assertions. Signed-off-by: Richard Yao <ryao@gentoo.org>
Inspection of a Ubuntu 14.04 x64 system revealed that the config file used to build the kernel image differs from the config file used to build kernel modules by the presence of CONFIG_DEBUG_INFO=y: root@zfs-dev:~# grep -E 'CONFIG_.*=' /boot/config-$(uname -r) | sort > /tmp/d1 root@zfs-dev:~# grep -E 'CONFIG_.*=' /usr/src/linux-headers-$(uname -r)/include/config/auto.conf | sort > /tmp/d2 root@zfs-dev:~# diff /tmp/d1 /tmp/d2 1017d1016 < CONFIG_DEBUG_INFO=y This in itself is insufficient to show that the kernel is built with debuginfo, but a cursory analysis of the debuginfo provided and the size of the kernel strongly suggests that it was built with CONFIG_DEBUG_INFO=y while the modules were not. Installing linux-image-$(uname -r)-dbgsym had no obvious effect on the debuginfo provided by either the modules or the kernel. The consequence is that issue reports from distributions such as Ubuntu and its derivatives build kernel modules without debuginfo contain nonsensical backtraces. It is therefore desireable to force generation of debuginfo, so we implement --enable-debuginfo. Since the build system can build both userspace components and kernel modules, the generic --enable-debuginfo option will force debuginfo for both. However, it also supports --enable-debuginfo=kernel and --enable-debuginfo=user for finer grained control. Enabling debuginfo for the kernel modules works by injecting CONFIG_DEBUG_INFO=y into the make environment. This is enables generation of debuginfo by the kernel build systems on all Linux kernels, but the build environment is slightly different int hat CONFIG_DEBUG_INFO has not been in the CPP. Adding -DCONFIG_DEBUG_INFO would fix that, but it would also cause build failures on kernels where CONFIG_DEBUG_INFO=y is already set. That would complicate its use in DKMS environments that support a range of kernels and is therefore undesireable. We could write a compatibility shim to enable CONFIG_DEBUG_INFO only when it is explicitly disabled, but we forgo doing that because it is unnecessary. Nothing in ZoL or the kernel uses CONFIG_DEBUG_INFO in the CPP at this time and that is unlikely to change. Enabling debuginfo for the userspace components is done by injecting -g into CPPFLAGS. This is not necessary because the build system honors the environment's CPPFLAGS by appending them to the actual CPPFLAGS used, but it is supported for consistency. Signed-off-by: Richard Yao <ryao@gentoo.org>
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Closing as unnecessary until I hear otherwise. |
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@behlendorf I am using this at my new job now. It is definitely something useful. |
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Closing. Won't merge. The SPL is being moved in to the ZFS tree so this will no longer be needed. The counterpart ZFS patches have been applied to master. |
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There are two commits here. The second implements --enable-debuginfo for distributions that build modules without debuginfo. The first is a refactor of --enable-debug based on an observation made during the development of the first that --enable-debug=true would paradoxically become --disable-debug. The order is reversed to make cherry picking easier should anyone want to backport only the change to --enable-debug's argument semantics.
This is the SPL version of openzfs/zfs#2734.