[PATCH AUTOSEL 6.17-5.4] kconfig/nconf: Initialize the default locale at startup

[Sasha Levin <sashal@kernel.org>]

From: Jakub Horký <jakub.git@horky.net>

[ Upstream commit 43c2931a95e6b295bfe9e3b90dbe0f7596933e91 ]

Fix bug where make nconfig doesn't initialize the default locale, which
causes ncurses menu borders to be displayed incorrectly (lqqqqk) in
UTF-8 terminals that don't support VT100 ACS by default, such as PuTTY.

Signed-off-by: Jakub Horký <jakub.git@horky.net>
Link: https://patch.msgid.link/20251014144405.3975275-2-jakub.git@horky.net
[nathan: Alphabetize locale.h include]
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

LLM Generated explanations, may be completely bogus:

Based on my comprehensive analysis using the available tools and
repository examination, here is my assessment:

## **ANSWER: YES**

This commit should be backported to stable kernel trees.

---

## Detailed Analysis:

### 1. **Code Changes Examined**

I examined the commit 707f0e1262828 (backport of upstream 43c2931a95e6b)
in the repository:

- **File**: `scripts/kconfig/nconf.c` (userspace build tool, not kernel
  runtime code)
- **Changes**:
  - Added `#include <locale.h>` at line 10 (alphabetically placed)
  - Added `setlocale(LC_ALL, "");` at line 1481 in main(), before any
    ncurses initialization
- **Total impact**: 3 lines added (1 include, 1 function call, 1 blank
  line)

### 2. **Semantic Analysis Tools Used**

- **Bash/Git**: Examined commit history, identified upstream commit
  (43c2931a95e6b), verified it's first included in v6.18-rc4
- **Read**: Examined the main() function structure in
  scripts/kconfig/nconf.c:1476-1509
- **Grep**: Searched for similar locale fixes across kconfig tools,
  found companion mconf fix (3927c4a1084c4)
- **WebSearch**: Researched the ncurses UTF-8/locale issue, confirmed
  this is a well-known problem with a standard solution

**Note**: I did not use mcp__semcode tools extensively because:
1. This is a userspace build tool, not kernel runtime code
2. The change is trivially small (2 effective lines)
3. The affected code has no complex call graphs or dependencies to
   analyze

### 3. **Impact Scope Analysis**

**What gets fixed:**
- ncurses menu borders in `make nconfig` display correctly in UTF-8
  terminals like PuTTY
- Before: borders show as "lqqqqk" (ACS characters in wrong encoding)
- After: borders show as proper box-drawing characters

**Who is affected:**
- Kernel developers/builders who use `make nconfig` in UTF-8 terminals
  without native VT100 ACS support
- Common scenario: PuTTY terminal connections

**Risk assessment:**
- **Extremely low risk**: `setlocale(LC_ALL, "")` is a standard C
  library function
- It simply initializes locale from environment variables (LANG, LC_ALL,
  etc.)
- Called before any ncurses initialization, following best practices
- No side effects on kernel build process or generated kernel

### 4. **Stable Tree Compliance Analysis**

This change meets all criteria for stable backporting:

✅ **Bug fix** - Fixes display corruption issue
✅ **Obviously correct** - Standard solution for well-known ncurses UTF-8
problem
✅ **Small scope** - Only 3 lines in one file
✅ **No new features** - Pure bug fix
✅ **User-visible improvement** - Better terminal display
✅ **Safe** - Uses standard library, no risk of regression
✅ **Self-contained** - No dependencies on other changes
✅ **Companion fix exists** - Similar fix applied to mconf (menuconfig)

### 5. **Supporting Evidence**

1. **Web research confirmed**: This is a documented ncurses issue where
   setlocale() must be called before initscr() for proper UTF-8 handling
   (Stack Overflow, multiple discussions)

2. **Pattern consistency**: Author Jakub Horký submitted matching fixes
   for both nconf and mconf, showing systematic resolution of the same
   issue across kconfig tools

3. **Already backported**: The commit shows `[ Upstream commit
   43c2931a95e6b ]` indicating stable maintainers have already accepted
   this for backporting

4. **Historical context**: Ancient commit 442ff70223328 "[PATCH] mconf.c
   needs locale.h" shows this has been a known requirement since early
   Linux kernel history

### 6. **Recommendation Rationale**

This is an **ideal stable backport candidate** because:
- Fixes real user-facing annoyance for kernel builders
- Trivially small and safe change
- No risk of regression or side effects
- Follows ncurses best practices
- Part of systematic fix across kconfig tools
- Change is build-time only, doesn't affect kernel runtime

The lack of an explicit "Cc: stable@vger.kernel.org" tag is not a
concern - stable maintainers correctly identified this as backport-
worthy, as evidenced by its presence in the stable tree with the "[
Upstream commit ]" annotation.

**Verdict: Strong YES for backporting to all applicable stable kernel
trees.**

 scripts/kconfig/nconf.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/scripts/kconfig/nconf.c b/scripts/kconfig/nconf.c
index ae1fe5f603270..521700ed71524 100644
--- a/scripts/kconfig/nconf.c
+++ b/scripts/kconfig/nconf.c
@@ -7,6 +7,7 @@
 #ifndef _GNU_SOURCE
 #define _GNU_SOURCE
 #endif
+#include <locale.h>
 #include <string.h>
 #include <strings.h>
 #include <stdlib.h>
@@ -1478,6 +1479,8 @@ int main(int ac, char **av)
 	int lines, columns;
 	char *mode;
 
+	setlocale(LC_ALL, "");
+
 	if (ac > 1 && strcmp(av[1], "-s") == 0) {
 		/* Silence conf_read() until the real callback is set up */
 		conf_set_message_callback(NULL);
-- 
2.51.0