NativeAOT: allow full-width 0x/0X-prefixed 64-bit hex env config values

[Copilot]

PR #127644 made 0x/0X valid for non-decimal NativeAOT config parsing, but CONFIG_VAL_MAXLEN still capped input at 16 chars, rejecting full-width values like 0xFFFFFFFFFFFFFFFF. This change aligns the textual length limit with the accepted syntax while preserving existing overlong-value rejection behavior.

• Config length limit update

  • Increased CONFIG_VAL_MAXLEN in src/coreclr/nativeaot/Runtime/RhConfig.h from 16 to 18 to allow 0x/0X + 16 hex digits.

• Comment accuracy

  • Updated nearby comments in RhConfig.h and RhConfig.cpp to describe max textual integer length semantics, not just raw hex digit count.

• Behavioral impact

  • Accepted now: 0xFFFFFFFFFFFFFFFF, 0XFFFFFFFFFFFFFFFF
  • Unchanged: inputs longer than prefix + 16 hex digits are still rejected by the existing buffer-length check (cchResult >= cchBuffer).

// RhConfig.h
#define CONFIG_VAL_MAXLEN 18              // "0x" prefix + 64-bit uint in hex

// RhConfig.cpp
TCHAR buffer[CONFIG_VAL_MAXLEN + 1]; // Max textual integer value plus a nul terminator.

Original prompt

Fix NativeAOT's environment config value maximum length after PR #127644 added support for 0x/0X prefixes in hex values.

Context:

• PR Fix NativeAOT hex config parser to handle 0x/0X prefix #127644 changed RhConfig::Environment::TryGetIntegerValue in src/coreclr/nativeaot/Runtime/RhConfig.cpp to accept and skip a leading 0x/0X prefix when parsing non-decimal values.
• CONFIG_VAL_MAXLEN is currently defined in src/coreclr/nativeaot/Runtime/RhConfig.h as 16 with the comment //64 bit uint in hex.
• TryGetIntegerValue uses TCHAR buffer[CONFIG_VAL_MAXLEN + 1] and rejects values where PalGetEnvironmentVariable returns cchResult >= cchBuffer.

Problem:

• A full-width 64-bit hex value without prefix is 16 characters, e.g. FFFFFFFFFFFFFFFF, and still fits.
• A full-width 64-bit hex value with prefix is 18 characters, e.g. 0xFFFFFFFFFFFFFFFF.
• Since prefixed hex values are now accepted syntax, CONFIG_VAL_MAXLEN == 16 incorrectly rejects valid full-width prefixed 64-bit values before parsing.

Task:

• Update the NativeAOT config parser length limit so values with a 0x/0X prefix plus up to 16 hex digits are accepted.
• Prefer a clear implementation, such as defining the textual max length as 18 or separating max hex digits from max prefix length if that reads better.
• Update nearby comments so they accurately describe the allowed input length.
• Add or update tests if an appropriate NativeAOT config parsing test location exists. At minimum, ensure the change is covered by existing relevant tests or add targeted coverage for 0xFFFFFFFFFFFFFFFF / 0XFFFFFFFFFFFFFFFF if feasible.
• Keep behavior for overlong values unchanged: values longer than prefix + 16 hex digits should still be rejected/truncated handling should remain safe.

Repository: dotnet/runtime
Related PR: #127644

The following is the prior conversation context from the user's chat exploration (may be truncated):

User: is value of CONFIG_VAL_MAXLEN still correct after this PR merged?

Assistant: No — not if 0x/0X is now considered valid syntax for 64-bit hex config values.

CONFIG_VAL_MAXLEN is still:

#define CONFIG_VAL_MAXLEN 16              //64 bit uint in hex

and the buffer is:

TCHAR buffer[CONFIG_VAL_MAXLEN + 1]; // hex digits plus a nul terminator.
const uint32_t cchBuffer = ARRAY_SIZE(buffer);
uint32_t cchResult = PalGetEnvironmentVariable(variableName, buffer, cchBuffer);
if (cchResult == 0 || cchResult >= cchBuffer)
    return false;

After the PR, a value like 0xFFFFFFFFFFFFFFFF is valid syntax conceptually — 16 hex digits for a full uint64_t, plus the 0x prefix — but it is 18 characters long. With CONFIG_VAL_MAXLEN == 16, the buffer only accepts up to 16 characters plus NUL, so this full-width prefixed value will be rejected before parsing.

So the constant should probably become something like:

#define CONFIG_VAL_MAXLEN 18 // "0x" prefix + 64-bit uint in hex

or split into clearer constants, e.g. max hex digits = 16 and max textual length = 18.

The merged PR fixes common values like 0xC0000000, but it leaves this max-length edge case inconsistent with the comment and with the newly accepted prefix syntax.

User: make a PR with the fix

Assistant: I’m waiting for your confirmation to proceed with creating the PR.

This pull request was created from Copilot chat.

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Pull request overview

This PR updates NativeAOT’s environment-variable integer config parsing to accept full-width 64-bit hex values when using the 0x/0X prefix, by increasing the fixed input buffer length and clarifying related comments.

Changes:

• Increase CONFIG_VAL_MAXLEN from 16 to 18 to allow "0x" + 16 hex digits.
• Update the TryGetIntegerValue local buffer comment to describe a textual-length bound rather than “hex digits”.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/coreclr/nativeaot/Runtime/RhConfig.h	Increases the max textual length constant for env integer config values to allow 0x/0X + 16 hex digits.
src/coreclr/nativeaot/Runtime/RhConfig.cpp	Updates the local buffer comment for env integer parsing to reflect the new textual max length semantics.

Comments suppressed due to low confidence (1)

src/coreclr/nativeaot/Runtime/RhConfig.cpp:55

• This change adjusts the accepted textual length for environment-provided integer config values, but I couldn’t find any targeted test that covers a full-width prefixed value like 0xFFFFFFFFFFFFFFFF/0XFFFFFFFFFFFFFFFF (and optionally an overlong value to confirm rejection). Adding a small NativeAOT-covered test case would help prevent regressions in this parsing edge case.

    TCHAR buffer[CONFIG_VAL_MAXLEN + 1]; // Max textual integer value plus a nul terminator.
    const uint32_t cchBuffer = ARRAY_SIZE(buffer);
    uint32_t cchResult = PalGetEnvironmentVariable(variableName, buffer, cchBuffer);
    if (cchResult == 0 || cchResult >= cchBuffer)
        return false;