qemu_x86_tiny places picolibc text outside of pinned.text

[keith-packard]

The qemu_x86_tiny test target creates linker scripts with a special .pinned.text region that should contain all code necessary for running outside of task context. However, this region does not end up including the text from picolibc.

To Reproduce
Steps to reproduce the behavior (requires changing lib/libc/Kconfig to enable picolibc for x86):

1. west build -b qemu_x86_tiny samples/kernel/condition_variables/simple -- -DCONFIG_PICOLIBC=y
2. cd build
3. ninja run
4. See failure (application hangs after printing Booting from ROM..)

Expected behavior
Sample should run correctly.

Impact
Prevents picolibc from being used with this one board.

Logs and console output
Here's the memory regions containing program text:

$ objdump -h zephyr/zephyr.elf | grep text
  0 boot.text     00001000  40100000  00100000  00001000  2**2
  5 pinned.text   00007000  40101000  00101000  00002000  2**0
 21 text          00001000  40117000  00517000  00011000  2**0

And here's where it stuck strncpy, which is called from z_setup_new_thread:

$ objdump -t zephyr/zephyr.elf | grep strncpy
40117142 g     F text	0000002b strncpy

Note that strncpy is in the text section, not the pinned.text section. This section is not
mapped for access when z_setup_new_thread is running at zephyr startup.

Environment (please complete the following information):

• OS: Linux
• Toolchain: Zephyr SDK 0.16.0-beta1
• Commit SHA or Version used: bf384bf

Additional context
Need to patch lib/libc/Kconfig to enable Picolibc use with this board:

$ git diff
diff --git a/lib/libc/Kconfig b/lib/libc/Kconfig
index 9e8b618975..20ccd9b4a6 100644
--- a/lib/libc/Kconfig
+++ b/lib/libc/Kconfig
@@ -18,7 +18,6 @@ config SUPPORT_MINIMAL_LIBC
 # Picolibc with C++ support in Zephyr SDK is handled by Zephyr SDK's own Kconfig.
 config PICOLIBC_SUPPORTED
        bool
-       depends on ARC || ARM || ARM64 || MIPS || RISCV
        depends on "$(ZEPHYR_TOOLCHAIN_VARIANT)" != "arcmwdt"
        depends on !(CPP && "$(ZEPHYR_TOOLCHAIN_VARIANT)" = "zephyr")
        default y

[keith-packard]

PR #54186 includes a patch that addresses this issue, 9c37171 -- I had thought that wasn't right because many tests continued to fail, but I've found other fixes for almost all of those in that same series.

[stephanosio]

@keith-packard Is this fixed by #54186?