Crash in PDFium (EXC_BAD_INSTRUCTION)

[UnluckyY1]

Hi 👋
Not sure which pdfrx version introduced this, but lately we’ve been receiving a lot of crash reports in Sentry related to PDFium on iOS.

Affected devices (from Sentry)
• iPhone10,3
• iPad7,5
• iPad6,12
• iPad7,12
• iPhone10,6

Affected iOS versions (from Sentry)
• iOS 17.7.10
• iOS 18.6.2
• iOS 16.7.12

EXC_BAD_INSTRUCTION
Exception 2, Code 1, Subcode 952090888
Crashed in non-app
PDFium
+0x2669ac
std::__Cr::locale::locale

PDFium
+0x0f1618
CPDFSDK_AppStream::SetAsTextField
In App
PDFium
+0x0ff208
CPDFSDK_Widget::ResetAppearance
In App
PDFium
+0x100eb8
CPDFSDK_Widget::OnLoad
In App
PDFium
+0x0fdf34
CPDFSDK_PageView::LoadFXAnnots
In App
PDFium
+0x0f735c
CPDFSDK_FormFillEnvironment::GetOrCreatePageView
In App
PDFium
+0x117f08
FPDF_FFLDraw
In App
App
+0x00950c
kDartVmSnapshotInstructions
In App
App
+0x927fa8
kDartIsolateSnapshotInstructions
In App
App
+0x927e34
kDartIsolateSnapshotInstructions
In App
App
+0x927ab4
kDartIsolateSnapshotInstructions
In App
App
+0x1f3704
kDartIsolateSnapshotInstructions
In App
App
+0x1f3668
kDartIsolateSnapshotInstructions
In App
App
+0x7ffebc
kDartIsolateSnapshotInstructions
In App
App
+0x79cfe8
kDartIsolateSnapshotInstructions
In App
App
+0x771a0c
kDartIsolateSnapshotInstructions
In App
App
+0x7718f4
kDartIsolateSnapshotInstructions
In App
App
+0x0f8dd0
kDartIsolateSnapshotInstructions
In App
App
+0x02c3e4
kDartIsolateSnapshotInstructions
In App
App
+0x972120
kDartIsolateSnapshotInstructions
In App
App
+0x04b968
kDartIsolateSnapshotInstructions
In App
App
+0x00baf0
kDartVmSnapshotInstructions
In App
Flutter
+0x53ff40
InternalFlutterGpu_Texture_AsImage
In App
Flutter
+0x54ce08
InternalFlutterGpu_Texture_AsImage
In App
Flutter
+0x551a10
InternalFlutterGpu_Texture_AsImage
In App
Flutter
+0x551824
InternalFlutterGpu_Texture_AsImage
In App
Flutter
+0x5ce948
InternalFlutterGpu_Texture_AsImage
In App
Flutter
+0x5aec3c
InternalFlutterGpu_Texture_AsImage
In App
Called from
libsystem_pthread
+0x0030e8
_pthread_start

[espresso3389]

@claude Could you investigate the potentional cause of the issue?

[claude]

Claude finished @espresso3389's task —— View job

---

Investigating PDFium Crash Issue

Analysis Todo List:

• Read repository setup instructions (CLAUDE.md and AGENTS.md)
• Analyze the crash stack trace pattern and identify crash location
• Examine PDFium integration in codebase (FPDF_FFLDraw usage)
• Research locale-related crashes and PDFium version information
• Provide comprehensive findings and actionable recommendations

Root Cause Analysis

Based on my investigation, this crash appears to be a locale-related memory corruption issue within PDFium's text field rendering system. Here's what I found:

Crash Pattern Analysis

The stack trace shows:

• Crash location: std::__Cr::locale::locale in PDFium
• Trigger path: FPDF_FFLDraw → CPDFSDK_Widget::OnLoad → CPDFSDK_AppStream::SetAsTextField
• Platform affected: iOS devices (iPhone/iPad) across multiple iOS versions (16.7.12, 17.7.10, 18.6.2)
• Error type: EXC_BAD_INSTRUCTION (indicates illegal instruction or memory corruption)

Technical Details

1. PDFium Version: Currently using chromium/7520
2. Crash Context: The crash occurs during form field rendering when FPDF_FFLDraw processes text field widgets
3. Locale Issue: The crash in std::__Cr::locale::locale suggests PDFium is trying to access locale information that may be corrupted or unavailable

Potential Causes

1. iOS Locale Inconsistencies:

   • iOS devices may have locale configurations that PDFium doesn't handle properly
   • Recent iOS versions might have changed locale behavior

2. Threading Issues:

   • PDFium runs in a background worker thread (lines 1220-1230 in pdfrx_pdfium.dart)
   • Locale objects may not be properly initialized in worker threads on iOS

3. Memory Corruption:

   • Form field processing might be accessing freed or uninitialized locale data
   • The crash occurs specifically when rendering text fields with appearance streams

Recommended Actions

1. Immediate Workaround:

   • Consider disabling form rendering on affected iOS versions:

   // In render() method, set:
   annotationRenderingMode: Platform.isIOS ? 
     PdfAnnotationRenderingMode.annotation : 
     PdfAnnotationRenderingMode.annotationAndForms

2. Investigate Further:

   • Check if PDFs with form fields consistently trigger this crash
   • Test with different locale settings on affected devices
   • Monitor if this affects specific PDF form types

3. Potential Fixes:

   • Update to a newer PDFium version (if available)
   • Initialize locale explicitly in the background worker thread
   • Add locale validation before calling FPDF_FFLDraw

4. Reporting:

   • Report this issue to the PDFium project with device/iOS version details
   • This appears to be a PDFium library bug rather than a pdfrx implementation issue

The crash is occurring at the PDFium library level during form field text processing, specifically when locale-dependent text formatting is attempted.

---

[espresso3389]

@UnluckyY1 Can you reproduce the issue on your side? Something is triggering the issue but I could not reproduce the issue. It may be specific to some PDF or specific to some pdfrx usage.

[UnluckyY1]

@espresso3389 This crash seems to happen only on older iOS devices, and unfortunately I’m not able to reproduce it on my side either. I tested all form fields using a PDF test file and everything worked as expected.

At the moment, the only lead I have is to ask one of the affected users to share the exact PDF that triggers the crash, I’m currently waiting for their response.

For reference, my use case is straightforward: I’m using PdfViewer.file(...).

[UnluckyY1]

@espresso3389 This might help: the last known working version is 2.2.7.
While reviewing the changelog, I noticed that version 2.2.10 introduced changes to pdfium_flutter (updated to pdfrx_engine 0.3.1 and pdfium_flutter 0.1.1).
This could be a good starting point to explain the issue. For now, I’ll revert to 2.2.7 and ask the affected user to test and confirm...

[UnluckyY1]

Just to update: downgrading back to version 2.2.7 completely resolves the PDF viewing crashes for our users, and our crash reports have stopped. This definitely seems like a regression introduced in the newer versions.

[espresso3389]

@UnluckyY1 Do you still see the issue with the latest version?