Improve diagnostic when gstd without 'debug'

[gshep]

Problem to Solve

When an execution of a program built with gstd/nodebug hits expect/assert/panic/unreachable/etc we get in the logs just short message 'probably unreachable reached`. It doesn't point whether it is program logic fails and where it was or an error rose on executor side.

Possible Solution

The idea is to introduce new syscall (or two):

+
+        pub fn gr_panic(file: u64, line: u32, column: u32);
+        pub fn gr_panic2(location: &core::panic::Location<'_>) -> !;
     }
 }
 // ...
+pub fn panic(loc: &core::panic::Location<'_>) -> ! {
+    unsafe {
+        sys::gr_panic(loc.file().as_ptr() as u64, loc.line(), loc.column());
+        sys::gr_panic2(loc)
+    }
+}

Implementation of gr_panic is just to put data to the log and interrupt the execution. gr_panic2 forces compiler to put Location instance somewhere and to provide a pointer to it. Panic handler could possibly look then like this:

--- a/gstd/src/common/handlers.rs
+++ b/gstd/src/common/handlers.rs
@@ -48,8 +48,11 @@ pub fn oom(_: Layout) -> ! {
#[cfg(not(debug_assertions))]
#[cfg(target_arch = "wasm32")]
#[panic_handler]
-pub fn panic(_: &PanicInfo) -> ! {
-    wasm32::unreachable();
+pub fn panic(panic_info: &PanicInfo) -> ! {
+    match panic_info.location() {
+        Some(loc) => gcore::msg::panic(loc),
+        _ => wasm32::unreachable(),
+    }
}

demo-panicker WAT looks with these changes applied the following way:

(module
 (type (;0;) (func (param i32)))
 (type (;1;) (func))
 (type (;2;) (func (param i64 i32 i32)))
 (import "env" "gr_panic" (func (;0;) (type 2)))
 (import "env" "gr_panic2" (func (;1;) (type 0)))
 (import "env" "memory" (memory (;0;) 17))
 (func (;2;) (type 1)
   i32.const 1048620
   call 3
   unreachable)
 (func (;3;) (type 0) (param i32)
   (local i32 i32)
   local.get 0
   call 5
   unreachable)
 (func (;4;) (type 1)
   i32.const 1048652
   call 3
   unreachable)
 (func (;5;) (type 0) (param i32)
   local.get 0
   call 6
   unreachable)
 (func (;6;) (type 0) (param i32)
   local.get 0
   call 7
   unreachable)
 (func (;7;) (type 0) (param i32)
   local.get 0
   i64.load32_u
   local.get 0
   i32.load offset=8
   local.get 0
   i32.load offset=12
   call 0
   local.get 0
   call 1
   unreachable)
 (export "handle" (func 2))
 (export "init" (func 4))
 (data (;0;) (i32.const 1048576) "I just panic every timepanicker/src/lib.rs\00\00\17\00\10\00\13\00\00\00\08\00\00\00\05\00\00\00Panic in init!\00\00\17\00\10\00\13\00\00\00\0e\00\00\00\05"))

wasm-proc could then process the binary, extract source file paths to the new info file (so called 'debug info') and squeeze data element a bit:

@@ -3,10 +3,9 @@
 (type (;1;) (func))
 (type (;2;) (func (param i64 i32 i32)))
 (import "env" "gr_panic" (func (;0;) (type 2)))
-  (import "env" "gr_panic2" (func (;1;) (type 0)))
 (import "env" "memory" (memory (;0;) 17))
 (func (;2;) (type 1)
-    i32.const 1048620
+    i32.const 1048576
   call 3
   unreachable)
 (func (;3;) (type 0) (param i32)
@@ -15,7 +14,7 @@
   call 5
   unreachable)
 (func (;4;) (type 1)
-    i32.const 1048652
+    i32.const 1048588
   call 3
   unreachable)
 (func (;5;) (type 0) (param i32)
@@ -34,9 +33,7 @@
   local.get 0
   i32.load offset=12
   call 0
-    local.get 0
-    call 1
   unreachable)
 (export "handle" (func 2))
 (export "init" (func 4))
-  (data (;0;) (i32.const 1048576) "I just panic every timepanicker/src/lib.rs\00\00\17\00\10\00\13\00\00\00\08\00\00\00\05\00\00\00Panic in init!\00\00\17\00\10\00\13\00\00\00\0e\00\00\00\05"))
+  (data (;0;) (i32.const 1048576) "\17\00\10\00\13\00\00\00\08\00\00\00\17\00\10\00\13\00\00\00\0e\00\00\00"))

However for this to work it is required somehow to force compiler to put all Locations in the new standalone section and file paths to the different one.

Notes

Disadvantage: too complicated

[gshep]

inspired by #1821

[breathx]

This syscall will cost some real funds and we should "lock" them for possible panic case at the start.
One more solution from my side here is to provide instead of Error::Unknown on the backend side something like Error::Unreachable(Option<.. last ext error ..>) with message like "reason is unknown, unreachable instruction called, but it may be due to: {ext.last_error} "

[grishasobol]

make also asserts in tests more precisely, see files:
pallets/gear/src/tests.rs
gtest/src/program.rs