Issue 1:
I'm experiencing a rather random segmentation fault in Julia 1.7.1 running a script using Plots.jl on a macOS Apple Silicon machine. I'm not sure where to start to isolate the problem.

signal (11): Segmentation fault: 11
in expression starting at /Users/gong/GitHub/covid19/plot_covid19.jl:95
^ at ./math.jl:0 [inlined]
bounding_order_of_magnitude at /Users/gong/.julia/packages/PlotUtils/xekml/src/ticks.jl:11
optimize_ticks_typed at /Users/gong/.julia/packages/PlotUtils/xekml/src/ticks.jl:197
unknown function (ip: 0x1167d539b)
jl_apply_generic at /Applications/Julia-1.7.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
#optimize_ticks#42 at /Users/gong/.julia/packages/PlotUtils/xekml/src/ticks.jl:154
optimize_ticks##kw at /Users/gong/.julia/packages/PlotUtils/xekml/src/ticks.jl:152
unknown function (ip: 0x1167d13f7)
jl_apply_generic at /Applications/Julia-1.7.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
optimal_ticks_and_labels at /Users/gong/.julia/packages/Plots/9C6z9/src/axes.jl:170
unknown function (ip: 0x1167d0423)
jl_apply_generic at /Applications/Julia-1.7.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
do_apply at /Applications/Julia-1.7.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
get_ticks at /Users/gong/.julia/packages/Plots/9C6z9/src/axes.jl:320
jl_apply_generic at /Applications/Julia-1.7.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
#get_ticks#95 at /Users/gong/.julia/packages/Plots/9C6z9/src/axes.jl:241
get_ticks at /Users/gong/.julia/packages/Plots/9C6z9/src/axes.jl:224 [inlined]
tick_padding at /Users/gong/.julia/packages/Plots/9C6z9/src/backends.jl:78
_update_min_padding! at /Users/gong/.julia/packages/Plots/9C6z9/src/backends.jl:108
jl_apply_generic at /Applications/Julia-1.7.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
iterate at ./generator.jl:47 [inlined]
_collect at ./array.jl:744
collect_similar at ./array.jl:653 [inlined]
map at ./abstractarray.jl:2849 [inlined]
_update_min_padding! at /Users/gong/.julia/packages/Plots/9C6z9/src/layouts.jl:290
jl_apply_generic at /Applications/Julia-1.7.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
iterate at ./generator.jl:47 [inlined]
_collect at ./array.jl:744
collect_similar at ./array.jl:653 [inlined]
map at ./abstractarray.jl:2849 [inlined]
_update_min_padding! at /Users/gong/.julia/packages/Plots/9C6z9/src/layouts.jl:290
jl_apply_generic at /Applications/Julia-1.7.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
prepare_output at /Users/gong/.julia/packages/Plots/9C6z9/src/plot.jl:224
show at /Users/gong/.julia/packages/Plots/9C6z9/src/output.jl:213 [inlined]
html at /Users/gong/.julia/packages/Plots/9C6z9/src/output.jl:63
jl_apply_generic at /Applications/Julia-1.7.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
savefig at /Users/gong/.julia/packages/Plots/9C6z9/src/output.jl:123
jl_apply_generic at /Applications/Julia-1.7.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
do_call at /Applications/Julia-1.7.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
eval_body at /Applications/Julia-1.7.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
jl_interpret_toplevel_thunk at /Applications/Julia-1.7.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
jl_toplevel_eval_flex at /Applications/Julia-1.7.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
jl_toplevel_eval_flex at /Applications/Julia-1.7.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
jl_toplevel_eval_in at /Applications/Julia-1.7.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
eval at ./boot.jl:373 [inlined]
include_string at ./loading.jl:1196
jl_apply_generic at /Applications/Julia-1.7.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
_include at ./loading.jl:1253
include at ./client.jl:451 [inlined]
top-level scope at ./timing.jl:220
jl_toplevel_eval_flex at /Applications/Julia-1.7.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
jl_toplevel_eval_flex at /Applications/Julia-1.7.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
jl_toplevel_eval_in at /Applications/Julia-1.7.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
eval at ./boot.jl:373 [inlined]
include_string at ./loading.jl:1196
jl_apply_generic at /Applications/Julia-1.7.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
_include at ./loading.jl:1253
include at ./client.jl:451
jl_apply_generic at /Applications/Julia-1.7.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
do_call at /Applications/Julia-1.7.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
eval_body at /Applications/Julia-1.7.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
jl_interpret_toplevel_thunk at /Applications/Julia-1.7.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
jl_toplevel_eval_flex at /Applications/Julia-1.7.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
jl_toplevel_eval_flex at /Applications/Julia-1.7.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
jl_toplevel_eval_in at /Applications/Julia-1.7.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
eval at ./boot.jl:373 [inlined]
eval_user_input at /Users/sabae/src/julia/usr/share/julia/stdlib/v1.7/REPL/src/REPL.jl:150
repl_backend_loop at /Users/sabae/src/julia/usr/share/julia/stdlib/v1.7/REPL/src/REPL.jl:244
start_repl_backend at /Users/sabae/src/julia/usr/share/julia/stdlib/v1.7/REPL/src/REPL.jl:229
#run_repl#47 at /Users/sabae/src/julia/usr/share/julia/stdlib/v1.7/REPL/src/REPL.jl:362
run_repl at /Users/sabae/src/julia/usr/share/julia/stdlib/v1.7/REPL/src/REPL.jl:349
jl_apply_generic at /Applications/Julia-1.7.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
#930 at ./client.jl:394
jfptr_YY.930_29470 at /Applications/Julia-1.7.app/Contents/Resources/julia/lib/julia/sys.dylib (unknown line)
jl_apply_generic at /Applications/Julia-1.7.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
jl_f__call_latest at /Applications/Julia-1.7.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
#invokelatest#2 at ./essentials.jl:716 [inlined]
invokelatest at ./essentials.jl:714 [inlined]
run_main_repl at ./client.jl:379
exec_options at ./client.jl:309
_start at ./client.jl:495
jl_sysimg_fvars_base at /Applications/Julia-1.7.app/Contents/Resources/julia/lib/julia/sys.dylib (unknown line)
jl_apply_generic at /Applications/Julia-1.7.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
true_main at /Applications/Julia-1.7.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
jl_repl_entrypoint at /Applications/Julia-1.7.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
Allocations: 168653373 (Pool: 168534659; Big: 118714); GC: 95

julia> versioninfo()
Julia Version 1.7.1
Commit ac5cc99908 (2021-12-22 19:35 UTC)
Platform Info:
OS: macOS (arm64-apple-darwin21.2.0)
CPU: Apple M1 Pro
WORD_SIZE: 64
LIBM: libopenlibm
LLVM: libLLVM-12.0.1 (ORCJIT, cyclone)

Issue 2:
I can reproduce it reliably, and have tracked it down to what seems like an ARM code generation bug.

julia> versioninfo()
Julia Version 1.7.0
Commit 3bf9d17731 (2021-11-30 12:12 UTC)
Platform Info:
OS: macOS (arm64-apple-darwin21.1.0)
CPU: Apple M1 Max
WORD_SIZE: 64
LIBM: libopenlibm
LLVM: libLLVM-12.0.1 (ORCJIT, cyclone)

julia> using WGLMakie

julia> fig=Figure()

julia> ax1 = Axis(fig[1, 1])

signal (11): Segmentation fault: 11
in expression starting at REPL[3]:1
^ at ./math.jl:0 [inlined]
bounding_order_of_magnitude at /Users/tlb/.julia/packages/PlotUtils/VgXdq/src/ticks.jl:14
optimize_ticks_typed at /Users/tlb/.julia/packages/PlotUtils/VgXdq/src/ticks.jl:161
#optimize_ticks#42 at /Users/tlb/.julia/packages/PlotUtils/VgXdq/src/ticks.jl:139 [inlined]
optimize_ticks##kw at /Users/tlb/.julia/packages/PlotUtils/VgXdq/src/ticks.jl:138 [inlined]
get_tickvalues at /Users/tlb/.julia/packages/Makie/gQOQF/src/makielayout/ticklocators/wilkinson.jl:21 [inlined]
get_tickvalues at /Users/tlb/.julia/packages/Makie/gQOQF/src/makielayout/ticklocators/wilkinson.jl:17 [inlined]
get_tickvalues at /Users/tlb/.julia/packages/Makie/gQOQF/src/makielayout/lineaxis.jl:459
get_ticks at /Users/tlb/.julia/packages/Makie/gQOQF/src/makielayout/lineaxis.jl:453
unknown function (ip: 0x12e27c4cb)
jl_apply_generic at /Applications/Julia-1.7arm.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
#191 at /Users/tlb/.julia/packages/Makie/gQOQF/src/makielayout/lineaxis.jl:187
unknown function (ip: 0x12e26d457)
jl_apply_generic at /Applications/Julia-1.7arm.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
do_apply at /Applications/Julia-1.7arm.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
#lift#61 at /Users/tlb/.julia/packages/Makie/gQOQF/src/interaction/nodes.jl:13
jl_apply_generic at /Applications/Julia-1.7arm.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
do_apply at /Applications/Julia-1.7arm.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
lift at /Users/tlb/.julia/packages/Makie/gQOQF/src/interaction/nodes.jl:10
jl_apply_generic at /Applications/Julia-1.7arm.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
#LineAxis#181 at /Users/tlb/.julia/packages/Makie/gQOQF/src/makielayout/lineaxis.jl:185
Type##kw at /Users/tlb/.julia/packages/Makie/gQOQF/src/makielayout/lineaxis.jl:3
unknown function (ip: 0x12e1e945b)
jl_apply_generic at /Applications/Julia-1.7arm.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
#layoutable#251 at /Users/tlb/.julia/packages/Makie/gQOQF/src/makielayout/layoutables/axis.jl:211
layoutable at /Users/tlb/.julia/packages/Makie/gQOQF/src/makielayout/layoutables/axis.jl:10 [inlined]
#_layoutable#11 at /Users/tlb/.julia/packages/Makie/gQOQF/src/makielayout/layoutables.jl:69 [inlined]
_layoutable at /Users/tlb/.julia/packages/Makie/gQOQF/src/makielayout/layoutables.jl:69 [inlined]
#_layoutable#10 at /Users/tlb/.julia/packages/Makie/gQOQF/src/makielayout/layoutables.jl:64
_layoutable at /Users/tlb/.julia/packages/Makie/gQOQF/src/makielayout/layoutables.jl:60 [inlined]
#_#9 at /Users/tlb/.julia/packages/Makie/gQOQF/src/makielayout/layoutables.jl:49 [inlined]
Layoutable at /Users/tlb/.julia/packages/Makie/gQOQF/src/makielayout/layoutables.jl:49
unknown function (ip: 0x12e1492d7)
jl_apply_generic at /Applications/Julia-1.7arm.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
do_call at /Applications/Julia-1.7arm.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
eval_body at /Applications/Julia-1.7arm.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
jl_interpret_toplevel_thunk at /Applications/Julia-1.7arm.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
jl_toplevel_eval_flex at /Applications/Julia-1.7arm.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
jl_toplevel_eval_flex at /Applications/Julia-1.7arm.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
jl_toplevel_eval_in at /Applications/Julia-1.7arm.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
eval at ./boot.jl:373 [inlined]
eval_user_input at /Users/administrator/src/julia/usr/share/julia/stdlib/v1.7/REPL/src/REPL.jl:150
repl_backend_loop at /Users/administrator/src/julia/usr/share/julia/stdlib/v1.7/REPL/src/REPL.jl:244
start_repl_backend at /Users/administrator/src/julia/usr/share/julia/stdlib/v1.7/REPL/src/REPL.jl:229
#run_repl#47 at /Users/administrator/src/julia/usr/share/julia/stdlib/v1.7/REPL/src/REPL.jl:362
run_repl at /Users/administrator/src/julia/usr/share/julia/stdlib/v1.7/REPL/src/REPL.jl:349
jl_apply_generic at /Applications/Julia-1.7arm.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
#930 at ./client.jl:394
jfptr_YY.930_43775 at /Applications/Julia-1.7arm.app/Contents/Resources/julia/lib/julia/sys.dylib (unknown line)
jl_apply_generic at /Applications/Julia-1.7arm.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
jl_f__call_latest at /Applications/Julia-1.7arm.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
#invokelatest#2 at ./essentials.jl:716 [inlined]
invokelatest at ./essentials.jl:714 [inlined]
run_main_repl at ./client.jl:379
exec_options at ./client.jl:309
_start at ./client.jl:495
jl_sysimg_fvars_base at /Applications/Julia-1.7arm.app/Contents/Resources/julia/lib/julia/sys.dylib (unknown line)
jl_apply_generic at /Applications/Julia-1.7arm.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
true_main at /Applications/Julia-1.7arm.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
jl_repl_entrypoint at /Applications/Julia-1.7arm.app/Contents/Resources/julia/lib/julia/libjulia-internal.1.7.dylib (unknown line)
Allocations: 163411336 (Pool: 163378481; Big: 32855); GC: 91

The line where it's crashing is:

while xspan < base^a * one_dt

Looking with lldb, it's segfaulting on an ldrb instruction (marked with a -> below). The base address in x19 derives from an adrp instruction, so it's some kind of immediate data relative to the PC.

Segfault is error: memory read failed for 0xee4e2400.

0x10fc9f878: stp d13, d12, [sp, #-0x70]!
0x10fc9f87c: stp d11, d10, [sp, #0x10]
0x10fc9f880: stp d9, d8, [sp, #0x20]
0x10fc9f884: stp x24, x23, [sp, #0x30]
0x10fc9f888: stp x22, x21, [sp, #0x40]
0x10fc9f88c: stp x20, x19, [sp, #0x50]
0x10fc9f890: stp x29, x30, [sp, #0x60]
0x10fc9f894: mov.16b v8, v1
0x10fc9f898: mov.16b v9, v0
0x10fc9f89c: fmul d10, d1, d1
0x10fc9f8a0: fmul d11, d10, d1
0x10fc9f8a4: fmov d0, #1.00000000
0x10fc9f8a8: mov w8, #0x3
0x10fc9f8ac: adrp x20, 0
0x10fc9f8b0: ldr x20, [x20, #0xa80]
0x10fc9f8b4: adrp x19, -137149
0x10fc9f8b8: add x19, x19, #0x410 ; =0x410
0x10fc9f8bc: fdiv d12, d0, d1
0x10fc9f8c0: b 0x10fc9f8d4
0x10fc9f8c4: mov.16b v0, v8
0x10fc9f8c8: fcmp d0, d9
0x10fc9f8cc: mov x8, x22
0x10fc9f8d0: b.le 0x10fc9f920
0x10fc9f8d4: sub x22, x8, #0x1 ; =0x1
0x10fc9f8d8: cmp x22, #0x4 ; =0x4
0x10fc9f8dc: b.hi 0x10fc9f8fc
0x10fc9f8e0: adr x8, #-0x1c
-> 0x10fc9f8e4: ldrb w9, [x19, x22]
0x10fc9f8e8: add x8, x8, x9, lsl #2
0x10fc9f8ec: fmov d0, #1.00000000
0x10fc9f8f0: br x8
0x10fc9f8f4: mov.16b v0, v12
0x10fc9f8f8: b 0x10fc9f8c8
0x10fc9f8fc: sub x8, x8, #0x2 ; =0x2
0x10fc9f900: scvtf d1, x8
0x10fc9f904: mov.16b v0, v8
0x10fc9f908: blr x20
0x10fc9f90c: b 0x10fc9f8c8
0x10fc9f910: mov.16b v0, v10
0x10fc9f914: b 0x10fc9f8c8
0x10fc9f918: mov.16b v0, v11
0x10fc9f91c: b 0x10fc9f8c8
0x10fc9f920: mov x19, #0x0
0x10fc9f924: sub x21, x22, #0x1 ; =0x1

I can see the calculation of x19 seems to be as instructed (the -137149 below is the argument to the adrp instruction). The adrp instruction masks the bottom 11 bits of the PC and adds its operand shifted left 12 bits.

(lldb) reg read x19
x19 = 0x00000000ee4e2410
(lldb) p/x (0x000000010fc9f8e4 & ~0xfff) + 0x1000*(-137149) + 0x410
(long) $9 = 0x00000000ee4e2410

And x22 is 2. But -137149 * 4096 seems like a strangely large offset! It's well outside the current code segment:

(lldb) reg read pc
pc = 0x000000010fc9f8e4
(lldb) mem region 0x000000010fc9f8e4
[0x000000010f99c000-0x000000010fd9c000) r-x

Thus, I suspect an error in ARM code generation for fetching PC-relative data.