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<a href="https://gitlab.rtems.org/matteo.concas">Matteo Concas</a>
commented on a
<a href="https://gitlab.rtems.org/rtems/rtos/rtems/-/issues/5383#note_135544">discussion</a>:
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<blockquote dir="auto" style="font-size: inherit; color: #626168; padding-top: 0.5rem; padding-bottom: 0.5rem; padding-left: 1rem; border-left-style: solid; margin: 0 0 0.5rem; border-color: #bfbfc3; border-width: 0 0 0 4px;" align="initial">
<p style="color: inherit; line-height: 1.5; margin: 0;">After looking at grmon4 a bit, it occurs to me that grmon does not support emulation</p>
</blockquote>
<p dir="auto" style="color: #3a383f; margin: 0 0 1rem;" align="initial">Indeed GRMON is only used to connect to hardware, we also have TSIM for simulation but we don't provide a trial version of the NOEL-V one.</p>
<p dir="auto" style="color: #3a383f; margin: 0 0 1rem;" align="initial">From more testing, I have noticed that this misaligned load is executed twice. The first time during system initialization when the DTB is parsed to find the end of the memory area in <code style='font-size: 90%; color: #18171d; word-wrap: break-word; border-radius: .25rem; background-color: #ececef; margin-top: 0; font-weight: inherit; white-space: break-spaces; overflow-wrap: break-word; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;'>bsp_memory_initialize()</code>. The CPU then goes to the exception handler as expected and <code style='font-size: 90%; color: #18171d; word-wrap: break-word; border-radius: .25rem; background-color: #ececef; font-weight: inherit; white-space: break-spaces; overflow-wrap: break-word; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;'>_Terminate()</code> is called. But, on system termination information is printed out to the console, to do that <code style='font-size: 90%; color: #18171d; word-wrap: break-word; border-radius: .25rem; background-color: #ececef; font-weight: inherit; white-space: break-spaces; overflow-wrap: break-word; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;'>printk()</code> which in turn will call <code style='font-size: 90%; color: #18171d; word-wrap: break-word; border-radius: .25rem; background-color: #ececef; font-weight: inherit; white-space: break-spaces; overflow-wrap: break-word; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;'>riscv_output_char_init()</code> and this function probe the FDT to find the console. During this parsing the same error is encountered but this time the exception handler is never entered.</p>
<p dir="auto" style="color: #3a383f; margin: 0 0 1rem;" align="initial">I suspect that is because of the <a href="https://docs.riscv.org/reference/isa/priv/smdbltrp.html" rel="nofollow noreferrer noopener" target="_blank" style="margin-top: 0;">double trap extension (Smdbltrp)</a> when combined with the <a href="https://docs.riscv.org/reference/isa/priv/rnmi.html#rnmi" rel="nofollow noreferrer noopener" target="_blank">Resumable Non-Maskable Interrupts extension (Smrnmi)</a>. In this case, if a double trap happens the RNMI handler should be called but RTEMS doesn't set this anywhere as far as I know meaning <code style='font-size: 90%; color: #18171d; word-wrap: break-word; border-radius: .25rem; background-color: #ececef; font-weight: inherit; white-space: break-spaces; overflow-wrap: break-word; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;'>pc</code> is set to whatever the reset value of the RNMI is (which is implementation defined). I need to check the CSR address in NOEL-V (also implementation defined) and then decide what we want to do in that case? Calling the exception handler a third time won't work obviously..</p>
<p dir="auto" style="color: #3a383f; margin: 0 0 1rem;" align="initial">Showing the double exception along with a register dump:</p>
<div class="gl-relative markdown-code-block js-markdown-code" style="margin-bottom: 0;">
<pre class="code highlight js-syntax-highlight language-plaintext" v-pre="true" style='display: block; font-size: 14px; color: #3a383f; line-height: 1.6em; overflow-x: auto; border-radius: .25rem; position: relative; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: break-all; word-wrap: break-word; background-color: #fbfafd; margin: 0 0 1rem; padding: 12px; border: 1px solid #dcdcde;'><code style='font-size: inherit; color: inherit; word-wrap: normal; word-break: keep-all; border-radius: .25rem; background-color: inherit; white-space: pre; margin-top: 0; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; overflow-wrap: normal; padding: unset;'><span id="LC1" class="line" lang="plaintext" style="margin-top: 0;">grmon4> bp _RISCV_Exception_handler</span>
<span id="LC2" class="line" lang="plaintext"> Software breakpoint 1 at <_RISCV_Exception_handler></span>
<span id="LC3" class="line" lang="plaintext"></span>
<span id="LC4" class="line" lang="plaintext">grmon4> run</span>
<span id="LC5" class="line" lang="plaintext"> CPU 0: Breakpoint 1 hit</span>
<span id="LC6" class="line" lang="plaintext"> 0x0000000000005c7c: eb010113 addi sp, sp, -336 <$xrv64i2p1_m2p0_a2p1_f2p2_d2p2_zicsr2p0_zmmul1p0_zaamo1p0_zalrsc1p0+0></span>
<span id="LC7" class="line" lang="plaintext"> CPU 1: Forced into debug mode</span>
<span id="LC8" class="line" lang="plaintext"> 0x00000000000000ac: ffdff06f j 0xa8</span>
<span id="LC9" class="line" lang="plaintext"></span>
<span id="LC10" class="line" lang="plaintext">grmon4> inst 10</span>
<span id="LC11" class="line" lang="plaintext"> TIME L P ADDRESS INSTRUCTION RESULT SYMBOL</span>
<span id="LC12" class="line" lang="plaintext"> 95902 1 M 000000000000e5e4 beqz a0, 0xe5f0 [0000000000000000] fdt_get_property_namelen_+0xe8</span>
<span id="LC13" class="line" lang="plaintext"> 95907 0 M 000000000000e5e8 lw a5, 12(sp) [000000000000000e] fdt_get_property_namelen_+0xec</span>
<span id="LC14" class="line" lang="plaintext"> 95907 1 M 000000000000e5ec beq a5, s3, 0xe65c [000000000000000e] fdt_get_property_namelen_+0xf0</span>
<span id="LC15" class="line" lang="plaintext"> 95982 0 M 000000000000e65c mv a2, s3 [000000000000000e] fdt_get_property_namelen_+0x160</span>
<span id="LC16" class="line" lang="plaintext"> 95983 0 M 000000000000e660 mv a1, s6 [0000000000018a70] fdt_get_property_namelen_+0x164</span>
<span id="LC17" class="line" lang="plaintext"> 95983 1 M 000000000000e664 jal ra, 0x13e38 [000000000000e668] fdt_get_property_namelen_+0x168</span>
<span id="LC18" class="line" lang="plaintext"> 95985 0 M 0000000000013e38 li a3, 7 [0000000000000007] memcmp+0x0</span>
<span id="LC19" class="line" lang="plaintext"> 95985 1 M 0000000000013e3c bgeu a3, a2, 0x13e5c [0000000000000007] memcmp+0x4</span>
<span id="LC20" class="line" lang="plaintext"> 95986 0 M 0000000000013e40 ld a4, 0(a0) [MISALIGNED LOAD 000000000001b5f9] memcmp+0x8</span>
<span id="LC21" class="line" lang="plaintext"> 96057 0 M 0000000000005c7c addi sp, sp, -336 [ BREAKPOINT ] $xrv64i2p1_m2p0_a2p1_f2p2_d2p2_zicsr2p0_zmmul1p0_zaamo1p0_zalrsc1p0+0x0</span>
<span id="LC22" class="line" lang="plaintext"></span>
<span id="LC23" class="line" lang="plaintext">grmon4> cont</span>
<span id="LC24" class="line" lang="plaintext"> CPU 0: Error mode (4, Load address misaligned)</span>
<span id="LC25" class="line" lang="plaintext"> 0x0000000030011000: 0000 illegal instruction</span>
<span id="LC26" class="line" lang="plaintext"> CPU 1: Forced into debug mode</span>
<span id="LC27" class="line" lang="plaintext"> 0x00000000000000ac: ffdff06f j 0xa8</span>
<span id="LC28" class="line" lang="plaintext"></span>
<span id="LC29" class="line" lang="plaintext">grmon4> inst 10</span>
<span id="LC30" class="line" lang="plaintext"> TIME L P ADDRESS INSTRUCTION RESULT SYMBOL</span>
<span id="LC31" class="line" lang="plaintext"> 103960 1 M 000000000000e428 ret [000000000000e42c] fdt_get_string+0x120</span>
<span id="LC32" class="line" lang="plaintext"> 103962 1 M 000000000000e5e4 beqz a0, 0xe5f0 [0000000000000000] fdt_get_property_namelen_+0xe8</span>
<span id="LC33" class="line" lang="plaintext"> 103967 0 M 000000000000e5e8 lw a5, 12(sp) [000000000000000a] fdt_get_property_namelen_+0xec</span>
<span id="LC34" class="line" lang="plaintext"> 103967 1 M 000000000000e5ec beq a5, s3, 0xe65c [000000000000000a] fdt_get_property_namelen_+0xf0</span>
<span id="LC35" class="line" lang="plaintext"> 103974 0 M 000000000000e65c mv a2, s3 [000000000000000a] fdt_get_property_namelen_+0x160</span>
<span id="LC36" class="line" lang="plaintext"> 103975 0 M 000000000000e660 mv a1, s6 [0000000000018858] fdt_get_property_namelen_+0x164</span>
<span id="LC37" class="line" lang="plaintext"> 103975 1 M 000000000000e664 jal ra, 0x13e38 [000000000000e668] fdt_get_property_namelen_+0x168</span>
<span id="LC38" class="line" lang="plaintext"> 103977 0 M 0000000000013e38 li a3, 7 [0000000000000007] memcmp+0x0</span>
<span id="LC39" class="line" lang="plaintext"> 103977 1 M 0000000000013e3c bgeu a3, a2, 0x13e5c [0000000000000007] memcmp+0x4</span>
<span id="LC40" class="line" lang="plaintext"> 103978 0 M 0000000000013e40 ld a4, 0(a0) [MISALIGNED LOAD 000000000001b5dc] memcmp+0x8</span>
<span id="LC41" class="line" lang="plaintext"></span>
<span id="LC42" class="line" lang="plaintext"></span>
<span id="LC43" class="line" lang="plaintext">grmon4> reg</span>
<span id="LC44" class="line" lang="plaintext"> a0: 000000000001b5dc t0: 00000000000000e0 s0: 0000000000000050</span>
<span id="LC45" class="line" lang="plaintext"> a1: 0000000000018858 t1: 0000000000000000 s1: 000000000001a3d8</span>
<span id="LC46" class="line" lang="plaintext"> a2: 000000000000000a t2: 0000000000014648 s2: 00000000000601c8</span>
<span id="LC47" class="line" lang="plaintext"> a3: 0000000000000007 t3: 0000000000000001 s3: 000000000000000a</span>
<span id="LC48" class="line" lang="plaintext"> a4: 000000000001b5e0 t4: 0000000000000000 s4: 0000000000000003</span>
<span id="LC49" class="line" lang="plaintext"> a5: 000000000000000a t5: 0000000000000000 s5: 0000000000000009</span>
<span id="LC50" class="line" lang="plaintext"> a6: 0000000000000000 t6: 0000000000000000 s6: 0000000000018858</span>
<span id="LC51" class="line" lang="plaintext"> a7: ffffffffffffffff s7: 0000000000000004</span>
<span id="LC52" class="line" lang="plaintext"> s8: 00000000000601ac</span>
<span id="LC53" class="line" lang="plaintext"> Machine mode sp: 0000000000060130 s9: 000000000001a460</span>
<span id="LC54" class="line" lang="plaintext"> FPU dirty state tp: 0000000000000000 s10: 0000000000000000</span>
<span id="LC55" class="line" lang="plaintext"> IRQ disabled gp: 000000000005bc48 s11: 0000000000000000</span>
<span id="LC56" class="line" lang="plaintext"></span>
<span id="LC57" class="line" lang="plaintext"> ra: 000000000000e668 <fdt_get_property_namelen_+0x16c></span>
<span id="LC58" class="line" lang="plaintext"> pc: 0000000030011000 illegal instruction</span>
<span id="LC59" class="line" lang="plaintext"></span>
<span id="LC60" class="line" lang="plaintext">grmon4> reg mtvec mepc mtval mcause mstatus</span>
<span id="LC61" class="line" lang="plaintext"> mtvec = 23676 (0x0000000000005c7c)</span>
<span id="LC62" class="line" lang="plaintext"> mepc = 81472 (0x0000000000013e40)</span>
<span id="LC63" class="line" lang="plaintext"> mtval = 112121 (0x000000000001b5f9)</span>
<span id="LC64" class="line" lang="plaintext"> mcause = 4 (0x0000000000000004)</span>
<span id="LC65" class="line" lang="plaintext"> mstatus = 9223376477850990592 (0x8000040a00007800)</span>
<span id="LC66" class="line" lang="plaintext"></span></code></pre>
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