Functions `__boot_from_prom` and `start_here_common` are "init code" in
the sense that they are only executed at boot time, nevertheless they
should not be tagged as __init since this will carry them to a different
section located at the very end of kernel text. If the TOC is not set up,
the kernel may not be able to tolerate a branch trampoline to reach the
init function.
Thus, these functions should be marked as `__ref` and the assembler must
be reminded to insert the code that follows into the last active section
by the use of the `.previous` directive. This will allow the powerpc
kernel to be built with CONFIG_SECTION_MISMATCH_WARN_ONLY disabled and
quieten the following modpost warnings during compilation:
WARNING: vmlinux.o(.text+0x2ad4): Section mismatch in reference from the
variable __boot_from_prom to the function .init.text:prom_init()
The function __boot_from_prom() references
the function __init prom_init().
This is often because __boot_from_prom lacks a __init
annotation or the annotation of prom_init is wrong.
WARNING: vmlinux.o(.text+0x2cd0): Section mismatch in reference from the
variable start_here_common to the function .init.text:start_kernel()
The function start_here_common() references
the function __init start_kernel().
This is often because start_here_common lacks a __init
annotation or the annotation of start_kernel is wrong.
Credits: code is based on commit <9c4e4c90ec24> ("powerpc/64: mark
start_here_multiplatform as __ref") and message is based on 2016 patch by
Nicholas Piggin:
https://lore.kernel.org/linuxppc-dev/20161222131419.18062-1-npig...@gmail.com/
Signed-off-by: Desnes A. Nunes do Rosario <desn...@linux.ibm.com>
---
arch/powerpc/kernel/head_64.S | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S
index 259be7f6d551..04b34397b656 100644
--- a/arch/powerpc/kernel/head_64.S
+++ b/arch/powerpc/kernel/head_64.S
@@ -540,6 +540,7 @@ __start_initialization_multiplatform:
b __after_prom_start
#endif /* CONFIG_PPC_BOOK3E */
+__REF
__boot_from_prom:
#ifdef CONFIG_PPC_OF_BOOT_TRAMPOLINE
/* Save parameters */
@@ -577,6 +578,7 @@ __boot_from_prom:
/* We never return. We also hit that trap if trying to boot
* from OF while CONFIG_PPC_OF_BOOT_TRAMPOLINE isn't selected */
trap
+ .previous
__after_prom_start:
#ifdef CONFIG_RELOCATABLE
@@ -983,6 +985,7 @@ start_here_multiplatform:
.previous
/* This is where all platforms converge execution */
+__REF
start_here_common:
/* relocation is on at this point */
std r1,PACAKSAVE(r13)
@@ -1003,6 +1006,7 @@ start_here_common:
/* Not reached */
BUG_OPCODE
+ .previous
/*
* We put a few things here that have to be page-aligned.
--
2.18.1
