Objects with storage-class specifier static and attribute __nocache not initialized before "program startup"

[jfischer-no]

Describe the bug

Objects with storage-class specifier static and attribute __nocache not initialized before "program startup".

To Reproduce

diff --git a/samples/hello_world/src/main.c b/samples/hello_world/src/main.c
index c550ab461cb..1ae4ac8a45e 100644
--- a/samples/hello_world/src/main.c
+++ b/samples/hello_world/src/main.c
@@ -5,10 +5,17 @@
  */
 
 #include <stdio.h>
+#include <zephyr/kernel.h>
+
+static uint64_t __nocache __aligned(4) abc123;
+static uint64_t __nocache __aligned(4) abc456 = 42;
 
 int main(void)
 {
-       printf("Hello World! %s\n", CONFIG_BOARD_TARGET);
+       printf("Hello World! %s %llu %llu\n", CONFIG_BOARD_TARGET, abc123, abc456);
+       abc123 = 1;
+       abc456 = 2;
+       printf("Hello World! %s %llu %llu\n", CONFIG_BOARD_TARGET, abc123, abc456);
 
        return 0;
 }

Steps to reproduce the behavior:

1. mkdir build; cd build
2. cmake -DBOARD=mimxrt1020_evk -DCONFIG_NOCACHE_MEMORY=y ~/zephyr-project/zephyr/samples/hello_world/
3. make
4. See output

Expected behavior
I think the nocache section should not be initialized, but that is probably not inline with the specification when storage-class specifier static is used, anyway it needs to be documented.

Impact
Unknown

Logs and console output

*** Booting Zephyr OS build v4.0.0-4626-ge783f69ebfae ***
Hello World! mimxrt1020_evk/mimxrt1021 1610636641 42
Hello World! mimxrt1020_evk/mimxrt1021 1 2

(reset)

*** Booting Zephyr OS build v4.0.0-4626-ge783f69ebfae ***
Hello World! mimxrt1020_evk/mimxrt1021 1 2
Hello World! mimxrt1020_evk/mimxrt1021 1 2

Environment (please complete the following information):

• OS:Linux
• Toolchain Zephyr SDK
• Commit SHA e783f69

[JarmouniA]

@jfischer-no __nocache alone doesn't suffice to place the object in nocache memory region, we need to know if CONFIG_NOCACHE_MEMORY is set or not.

zephyr/include/zephyr/linker/section_tags.h

Line 53 in e783f69

#if defined(CONFIG_NOCACHE_MEMORY)

[jfischer-no]

@jfischer-no __nocache alone doesn't suffice to place the object in nocache memory region, we need to know if CONFIG_NOCACHE_MEMORY is set or not.

zephyr/include/zephyr/linker/section_tags.h

Line 53 in e783f69
#if defined(CONFIG_NOCACHE_MEMORY)

yes, it was already in the description but not visible, fixed it.

[github-actions]

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[jachatzi]

@jfischer-no should be fixed on main now, as #87826 has been merged.

[jfischer-no]

@jfischer-no should be fixed on main now, as #87826 has been merged.

Thank you.