__attribute__((section(“name”))) usage?

Question

I have ran through code that use _ attribute _((section(\"name\")). I understand that for gcc compiler this allows you to tell the linker to put the object cre

Answer 1

From a usecase point of view, there are lots of different types of .data, like:

• data local to a specific CPU and/or NUMA node
• data shared between contexts (like user/kernelspace, as are the .vdso or vsyscall pages. Or, another example, bootloader and kernel)
• readonly data or other data with specific access mode/type restrictions (say, cacheability or cache residency - the latter can be specificed on some ARM SoCs)
• data that persists "state transitions" (such as hibernation image loads, or crash kernel / fast reboot reinitializations)
• data with specific lifetimes/lifecycles (only used in specific stages during boot or during operation, write-once data)
• data specific to a particular kernel subsystem or particular kernel module
• "code colocated" data (addressing offsets in x64 are plus/minus 2GB so if you want RIP-relative addressing, the data must be within that range of your currently executing code)
• data mapped to some specific hardware register space VA range

So in the end it's often about attributes (the word here used in a more generic sense than what __attribute__(...) allows you to state from within gcc sourcecode. Whether another section is needed and/or useful is ... in the eye of the beholder - the system designer, that is.

The availabiltiy of the section attribute, therefore, allows for flexibility and that is, IMHO, a good thing.