Fred Peterson
2016-01-05 23:36:34 UTC
Linaro TCWG,
In newer toolchains that are built with ABE, libc.a contains a lot of debugging information, including the paths to the source files on the build machine. I think that's because ABE builds the libraries with -g and never strips out the debug information. I verified this with both the 4.9-2015.05 and 5.2-2015.11 binary releases with the command:
arm-linux-gnueabih-objdump -g libc.a | grep '\.c'
In older toolchains that were built with crosstool-ng, libc.a did not contain the paths to the source files. I guess crosstool-ng either didn't build the libraries with -g, or it stripped out the debug information later. I verified this with the 4.9-2014.09 binary release.
I'm not sure whether this change was intentional, or just an oversight during the switchover to ABE. Regardless, it makes the libraries a lot bigger, and it potentially affects the end user during debugging.
The source files of libc, etc. are not typically included with the binary releases. So, when a user of an ABE-built binary release chooses to step into an extern function of libc, gdb will search for the source file. It likely won't be able to access the source file along the same path that worked for the build machine, so it will search its list of source directories. Ultimately, unless the user has downloaded the source files, gdb will likely display a message like "printf.c: No such file or directory".
In contrast, when a user of a crosstool-ng-built toolchain tries to step into an extern function of libc, gdb will be unaware of the name of the source file. As a result, the user will not get a message about a missing file.
So, should the toolchains' libraries really contain debug information? I think it could be useful for a theoretical multilib folder that covers a -g option. On the other hand, for the usual release builds, isn't the debug information a waste of space and a source of confusion?
Thanks,
Fred Peterson
Engineer - Developer Tools
NXP Semiconductors
In newer toolchains that are built with ABE, libc.a contains a lot of debugging information, including the paths to the source files on the build machine. I think that's because ABE builds the libraries with -g and never strips out the debug information. I verified this with both the 4.9-2015.05 and 5.2-2015.11 binary releases with the command:
arm-linux-gnueabih-objdump -g libc.a | grep '\.c'
In older toolchains that were built with crosstool-ng, libc.a did not contain the paths to the source files. I guess crosstool-ng either didn't build the libraries with -g, or it stripped out the debug information later. I verified this with the 4.9-2014.09 binary release.
I'm not sure whether this change was intentional, or just an oversight during the switchover to ABE. Regardless, it makes the libraries a lot bigger, and it potentially affects the end user during debugging.
The source files of libc, etc. are not typically included with the binary releases. So, when a user of an ABE-built binary release chooses to step into an extern function of libc, gdb will search for the source file. It likely won't be able to access the source file along the same path that worked for the build machine, so it will search its list of source directories. Ultimately, unless the user has downloaded the source files, gdb will likely display a message like "printf.c: No such file or directory".
In contrast, when a user of a crosstool-ng-built toolchain tries to step into an extern function of libc, gdb will be unaware of the name of the source file. As a result, the user will not get a message about a missing file.
So, should the toolchains' libraries really contain debug information? I think it could be useful for a theoretical multilib folder that covers a -g option. On the other hand, for the usual release builds, isn't the debug information a waste of space and a source of confusion?
Thanks,
Fred Peterson
Engineer - Developer Tools
NXP Semiconductors