[Skiboot] [PATCH v3] Fix array-bound compilation warnings

[Nicholas Piggin]

Excerpts from Abhishek Singh Tomar's message of January 24, 2022 11:56 pm:
> Resolves : the warray bounds warning during compilation
> 
> /build/libc/include/string.h:34:16: warning: '__builtin_memset' offset [0, 2097151] is out of the bounds [0, 0] [-Warray-bounds]
> 34 | #define memset __builtin_memset
> hw/fsp/fsp.c:1855:9: note: in expansion of macro 'memset'
> 1855 | memset(fsp_tce_table, 0, PSI_TCE_TABLE_SIZE);
> 
> use volatile pointer to avoid optimization introduced with gcc-11 on constant
> address assignment to pointer.

Thanks for persisting with this. I'm not sure it's quite the right way 
to fix it. It might be something to ask on the gcc at gcc.gnu.org mailing
list.

C is supposed to be usable for embedded systems where you expect to be 
working with a lot of data that's outside the visibility of the 
compiler. Yet we don't want to disable array bounds checking entirely.

The volatile just seems a bit clunky but I'm not sure what a better
option is. Declaring the addresses in the linker script maybe gives us
a better result including bounds checking for the memory? Will take a
little more work though, e.g.:

Thanks,
Nick

---

diff --git a/core/fast-reboot.c b/core/fast-reboot.c
index fedfa88cc..3fec6ab8a 100644
--- a/core/fast-reboot.c
+++ b/core/fast-reboot.c
@@ -304,6 +304,9 @@ static void cleanup_cpu_state(void)
 /* Entry from asm after a fast reset */
 void __noreturn fast_reboot_entry(void);
 
+extern char kernel_load_base[KERNEL_LOAD_SIZE];
+extern char initramfs_load_base[INITRAMFS_LOAD_SIZE];
+
 void __noreturn fast_reboot_entry(void)
 {
 	struct cpu_thread *cpu = this_cpu();
@@ -425,8 +428,8 @@ void __noreturn fast_reboot_entry(void)
 		 * Mambo may have embedded payload here, so don't clear
 		 * it at all.
 		 */
-		memset(KERNEL_LOAD_BASE, 0, KERNEL_LOAD_SIZE);
-		memset(INITRAMFS_LOAD_BASE, 0, INITRAMFS_LOAD_SIZE);
+		memset(kernel_load_base, 0, KERNEL_LOAD_SIZE);
+		memset(initramfs_load_base, 0, INITRAMFS_LOAD_SIZE);
 	}
 
 	/* Start preloading kernel and ramdisk */
diff --git a/skiboot.lds.S b/skiboot.lds.S
index 058848fa9..92726d7e1 100644
--- a/skiboot.lds.S
+++ b/skiboot.lds.S
@@ -251,6 +251,9 @@ SECTIONS
 
 	DEBUG_SECTIONS
 
+	kernel_load_base = 0x20000000;
+	initramfs_load_base = 0x20000000 + 0x08000000;
+
 	/* Discards */
 	/DISCARD/ : {
 		*(.note.GNU-stack)