casaroli commented on code in PR #19942:
URL: https://github.com/apache/nuttx/pull/19942#discussion_r3912607045
##########
libs/libc/elf/elf_load.c:
##########
@@ -573,14 +685,10 @@ int libelf_load(FAR struct mod_loadinfo_s *loadinfo)
}
loadinfo->gotindex = libelf_findsection(loadinfo, ".got");
- if (loadinfo->gotindex >= 0)
+ if (loadinfo->gotindex >= 0 || loadinfo->fdpic)
Review Comment:
done.
##########
libs/libc/elf/elf_load.c:
##########
@@ -729,14 +912,10 @@ int libelf_load_with_addrenv(FAR struct mod_loadinfo_s
*loadinfo)
}
loadinfo->gotindex = libelf_findsection(loadinfo, ".got");
- if (loadinfo->gotindex >= 0)
+ if (loadinfo->gotindex >= 0 || loadinfo->fdpic)
Review Comment:
done
##########
binfmt/Kconfig:
##########
@@ -60,6 +60,38 @@ config ELF_STACKSIZE
default DEFAULT_TASK_STACKSIZE
---help---
This is the default stack size that will be used when starting
ELF binaries.
+
+config FDPIC
+ bool "FDPIC modules"
+ default n
+ select PIC
+ depends on ARCH_HAVE_ELF_FDPIC
+ ---help---
+ Load ELF modules built for the FDPIC ABI.
+
+ An FDPIC module places its read-only and writable segments
+ independently, so its text can be executed directly out of flash
+ while only the writable segment is copied to RAM, once per
running
+ instance. A filesystem that can show its media, such as XIPFS
or
+ ROMFS, gives that result. On any other filesystem the loader
copies
+ the text to RAM, and the module runs but shares nothing.
+
+ Building a module needs an arm-uclinuxfdpiceabi linker. The
stock
+ arm-none-eabi compiler emits correct FDPIC objects for both C
and
+ C++, so only the link needs it.
+
+ What this adds over the position independent ELF support already
+ present is a function pointer that carries its own data base,
as a
+ two word descriptor rather than a bare code address. That is
what
+ lets a module be called back on a thread it did not create,
such as
+ the work queue worker that runs a SIGEV_THREAD notification.
+
+ Selecting this makes ten libc and sched entry points that can
+ accept a callback from a module resolve such a descriptor before
+ storing or branching to it. Each costs a register read and a
+ branch on a path that is not hot.
+
+ FDPIC is specified only for ARM Thumb-2.
Review Comment:
done
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